Belief in qadar (predestination) is one of the most basic principles of faith, without which a person's belief is incomplete. Visit the following link for a list of hadith regarding qadar. http://www.usc.edu/dept/MSA/fundamentals/tawheed/abdulwahab/KT1-chap-57.html
What is Qadar?
Many scholars have attempted to define what Qadar is.
The root of qadar is qadara. In Arabic it is said "Qadartu ash-shay'a qadran (or qadaran) (I evaluated the thing)," if one knows its quantity and other attributes. (Fath al-Baari by Ibn Hajar al-'Asqalani, 1/118, Cited in Umar Al Ashqar, Divine Will and Predestination in the Light of Quran and Sunnah, p 33)
In Arabic, qadar means decree, judgement, ultimate destiny. Taqdeer means to think about how to sort things out. (Al Qaamoos al-Muheet by Al-Fayroozabaadi, p. 591, Cited in Umar Al Ashqar, Divine Will and Predestination in the Light of Quran and Sunnah, p 33)
In a technical sense, qadar means, "something of which there was prior knowledge, one of the things which was written by the Pen when it wrote down everything that was going to happen for the rest of eternity, when Allah decreed the affairs of all His creation and what would happen before it happened. He knew that these things would happen at certain times that were known to Him, and in specific ways, and so things happen in the way that He has decreed. ('Aqeedat as-Safaareeni, 1/348, Cited in Umar Al Ashqar, Divine Will and Predestination in the Light of Quran and Sunnah, p 33)
Ibn Hajar said in his definition: "What is meant is that Allah knows how things will be and when they will happen, before He initiates them. Then He creates that which He already knows will happen. Hence everything that happens stems from His knowledge, power and will. (Fath al-Baari, 1/118, Cited in Umar Al Ashqar, Divine Will and Predestination in the Light of Quran and Sunnah, p 33)
Ibn Hajar al-'Asqalani said that the word qadar implies ability or power, and the object of that ability, which exists in the knowledge of Allah. (Fath al-Baari, 11/477, Cited in Umar Al Ashqar, Divine Will and Predestination in the Light of Quran and Sunnah, p 23)
Imam Ahmad was asked about qadar. He said "Qadar is the power of Allah." (Majmoo' al-Fataawa Shaykh al-Islam, 8/308, Cited in Umar Al Ashqar, Divine Will and Predestination in the Light of Quran and Sunnah, p 24)
Ibn Abbas said: qadar is the essence of Tawheed. Whoever worships Allah, the Almighty, Alone and believes in qadar has perfected his Tawheed, but whoever worships Allah Alone but does not believe in qadar, destroys his Tawheed by this disbelief. (Majmoo' al-Fataawa Shaykh al-Islam, 8/258, Cited in Umar Al Ashqar, Divine Will and Predestination in the Light of Quran and Sunnah, p 24)
Rational Evidence that Allah knew about the qadar of His creation before He created it
The truth is that the existence of this universe and every creature in it clearly indicates that Allah had knowledge of it before He created it. "For it is impossible that He could create these things without knowing about them, because He creates things by His Will, and will requires a preconceived idea about the desired thing. This preconceived idea about the desired thing is knowledge of the desired thing. So creation requires will and will requires knowledge, so creation requires knowledge." (Sharh at-Tahaawiyah, p 148, Cited in Umar Al Ashqar, Divine Will and Predestination in the Light of Quran and Sunnah, p 42)
Moreover, "The created beings which exist in it are made in a proper and perfect manner which implies that the One Who made them must have knowledge of the, because such perfect work could not have been done by one who has no knowledge" (Sharh at-Tahaawiyah, p 148, Cited in Umar Al Ashqar, Divine Will and Predestination in the Light of Quran and Sunnah, p 42)
The scholars also use a kind of analogy as evidence for the knowledge of Allah: "Among His creation are those who have knowledge, and knowledge is an attribute of perfection, so it is impossible for the Creator not to have knowledge." This can be proven in two ways:
(1) It may be said: we know that the Creator is inevitably more perfect than His creation, and that the One Who must exist (Allah) is more perfect than one who may or may not exist (creature). If we assume that he former has knowledge whilst the latter does not, then the One Who has knowledge is more perfect. If the Creator does not have knowledge, this would imply that the one who may or may not exist (creature) is more perfect than Him, and this is impossible.
(2) Every type of knowledge that the created being has, comes from Allah, and it is impossible for the One Who created these beings with some attributes of perfection to be devoid of perfection; He is more entitled to perfection than they are, because whatever attributes of perfection the created beings are known to have, the Creator is more entitled to them, and whatever imperfections the created beings are above having, the Creator is more entitled to be above them and free of them. (Sharh at-Tahaawiyah, p 148, Cited in Umar Al Ashqar, Divine Will and Predestination in the Light of Quran and Sunnah, p 42)
All of this evidence may be summed up in the verse
Should He not know what He created? And He is the Subtile, the Aware.
Benefits of believing in Qadar
1) Belief in Qadar is a Means of Ridding Oneself of Shirk
The Magians (Zoroastrians) claimed that the Light was the creator of good, and Darkness was the creator of evil.
Those among this ummah who claimed that Allah does nto create the deeds of his slaves, or that He does not create the misguided deeds, are claiming that there are creators other than Allah.
The one who believes in qadar affirms that this universe and everything in it was created by One God; those who do not believe this imply that there are other gods and lords besides Allah. (Umar Al Ashqar, Divine Will and Predestination in the Light of Quran and Sunnah, p 139-140)
2) Adhering To The True Path During Both Times of Ease and Times of Difficulty
Belief in qadar makes a person persist in his adherence to the straigh path, so that he is not reckless at times of ease, and does not fall into despair when calamity strikes, for he knows that everything good that happens to him comes from Allah, and is not because of his intelligence or good planning. (Umar Al Ashqar, Divine Will and Predestination in the Light of Quran and Sunnah, p 140)
And whatever favor is (bestowed) on you it is from Allah; then when evil afflicts you, to Him do you cry for aid.
And when trials and tribulations befall a person, he knows that this is happening by the decree of Allah, as a test from Him, so he does not panic or despair, rather he seeks the reward of Allah and bears it with patience, and this faith brings contentment and tranquility to the heart of the believer. (Umar Al Ashqar, Divine Will and Predestination in the Light of Quran and Sunnah, p 142)
No evil befalls on the earth nor in your own souls, but it is in a book before We bring it into existence; surely that is easy to Allah: So that you may not grieve for what has escaped you, nor be exultant at what He has given you; and Allah does not love any arrogant boaster:
And Allah Praises His slaves,
Surah 2: 156-157
Who, when a misfortune befalls them, say: Surely we are Allah's and to Him we shall surely return. Those are they on whom are blessings and mercy from their Lord, and those are the followers of the right course.
Links That Talk About Qadar
Besides writing a lengthy article. I have seen that the issues have already been addressed and talked about. Here is a list of links that people can visit to know more about the topic.
http://www.islamonline.net/servlet/Satellite?cid=1131347555693&pagename=IslamOnline-English-Ask_Scholar%2FFatwaE%2FFatwaEAskTheScholar (concisely talking about all the main points regarding predestination)
http://www.islamonline.net/servlet/Satellite?pagename=IslamOnline-English-Ask_Scholar/FatwaE/FatwaE&cid=1119503544138 (very good explanation on how Allah has given us free will and what it means that Allah "wills" us to do something)
http://www.islamonline.net/servlet/Satellite?pagename=IslamOnline-English-Ask_Scholar/FatwaE/FatwaE&cid=1119503543728 and http://www.islamonline.net/servlet/Satellite?pagename=IslamOnline-English-Ask_Scholar/FatwaE/FatwaE&cid=1119503545592 (someone asking a question about whether we need to strive because everything is predestined)
http://www.islamatschool.org.uk/GC/GCSETopicsPages/Suffering.pdf (scroll down to point number 6)
http://www.understanding-islam.com/related/questionsarticles.asp?sscatid=18 (several questions regarding predestination are asked and answered)
http://www.answering-christianity.com/quran/ma_guiding.htm (About the verses in the Quran where it says that God guides whom he wills)
http://www.free-minds.org/articles/gods_system/destiny.htm (excellent article, but warning: this website is an anti hadith site. however, this article has nothing wrong it)
There was so much more I could have talked about but I kept the article concise. If people are truly interested, I strongly suggest that people buy this book http://onlineislamicstore.com/b7895.html. There are probably many things that people might not understand about Qadar. So please feel free to email me and ask me at firstname.lastname@example.org