To reject belief in Divine Preordainment (Qadar), both the good and the evil of it, is disbelief.
"Faith (Iman) is to believe in Allah, His Angels, His Books, His Messengers and to believe in Qadar (Divine Preordainment), both the good and evil thereof." (Hadith)
"No slave will (truly) believe until he believes in Qadar, its good and bad from Allah and until he knows that what has befallen him was not going to pass him by, and what has passed him by was not going to befall him." (Hadith)
God has created everything with known measure, sustenance and ordainment.
And there is not a thing, but with Us are the supplies thereof. And We send it not down except in a known measure. (Quran 15:21)
Verily, We have created all things with Qadar (Divine Preordainment). (Quran 54:49)
God has Eternal Knowledge regarding all aspects of destinies for all of creation, past, present and future.
And with Him are the keys of the Unseen, none knows them but He. And He knows whatever there is in the land and in the sea; not a leaf falls, but He knows it. There is not a grain in the darkness of the Earth, neither anything fresh or dry, but it is written in the Clear Record. (Quran 6:59)
Do you not know, that Allah knows all that is in the Heaven and in the Earth? Verily! It is all in the Book. Verily! That is easy for Allah. (Quran 22:70)
God has Recorded the fates of every created thing by Writing it in a Book called the "Lawhul-Mahfooz" (The Preserved Tablet).
No calamity befalls on the Earth or in yourselves but it is inscribed in the Book of Decrees, before We bring it into existence. Verily, that is easy for Allah. (Quran 57:22)
Nay! This is a Glorious Qur'aan, (inscribed) in Lawhul-Mahfooz (the Preserved Tablet). (Quran 85:22)
God Wrote all that would ever occur 50,000 years before creating the Heavens and the Earth.
"Allah had Written the ordained measures (and their due proportions) of the creation, fifty thousand years before the creation of the Heavens and the Earth, and His Throne was on water." (Hadith)
Nothing can ever happen unless God Permits and Wills it.
"When you invoke, invoke Allah Alone, and when you ask for help, ask Allah Alone. And know that if the nation (meaning mankind and the Jinn) came together to bring you benefit, they can never bring you any benefit except that which Allah has Written for you. And if they came together to harm you, they will never be able to harm you, except what Allah has Written for you. The pens have already been raised (and stopped writing) and the pages have dried." (Hadith)
God is the Creator of all creation and what it possesses of attributes and actions.
He has created everything, and has measured it exactly according to its due measurements. (Quran 25:2)
He (Abraham) said (to his people): "Do you worship that which you (yourselves) carve? While Allah has created you and what you make." (Quran 37:95-96)
All of us have taken a Covenant with God in our Pre-history before we were born.
"When Allah created Adam, He took a Covenant from him in a place called Na’maan on the day of Arafah (9th of Dhul Hijjah, the day preceding the Eid celebration following Hajj), then He extracted from him all of his descendants who would be born until the end of the world, generation after generation, and spread them out in front of Him in order to take a Covenant from them also. He spoke to them Face to face saying: "Am I not your Lord?" and they all replied, "Yes, we testify to it!" Allah then explained why He had all of Mankind bear witness that He was their Creator and only True God worthy of worship. He said, "That was in case you (Mankind) should say on the Day of Resurrection, "Surely we were unaware of all this. We had no idea that You, Allah, were our God. No one told us that we were supposed to worship only You." Allah went on to explain that it was also in case you should say: "It was our ancestors who made partners (with Allah) and we were only their descendants; will You (Allah), then destroy us for what those liars did?" [The Prophet’s صلى الله عليه وسلم explanation of the Qur'an, verses 7:172-173] (Hadith)
God has already determined who will deserve to go to Paradise or Hell.
"The creation of every one of you starts with the process of collecting the material for his body within forty days and forty nights in the womb of his mother. Then he becomes a clot of thick blood for a similar period (40 days) and then he becomes like a piece of flesh for a similar period. Then an Angel is sent to him (by Allah) and the Angel is allowed (ordered) to write four things; his livelihood, his (date of) death, his deeds, and whether he will be a wretched one (ending up in Hell) or a blessed one (ending up in Paradise) and then the soul is breathed into him. So one of you may do (good) deeds characteristic of the people of Paradise so much that there is nothing except a cubit between him and Paradise but then what has been Written for him decides his behavior and he starts doing (evil) deeds characteristic of the people of Hell and (ultimately) enters Hell; and one of you may do (evil) deeds characteristic of the people of Hell so much so that there is nothing except a cubit between him and Hell, then what has been Written for him decides his behavior and he starts doing (good) deeds characteristic of the people of Paradise (and ultimately) enters Paradise." (Hadith)
"Allah created John the son of Zakariyah as a believer in his mother’s womb and He created Pharaoh as a disbeliever in his mother’s womb." (Hadith)
Muslims are forbidden to debate about Divine Decree.
"When my Companions are mentioned, hold back; when the stars (i.e. Astrology) are mentioned, hold back; and when Allah’s Decree (Qadar) is mentioned, hold back." (Hadith)
When the Prophet صلى الله عليه وسلم heard some of his Companions disputing about Qadar he became angry and said, "Were you commanded to do this? Or was I sent to you in order to do this (dispute)? Verily it was such disputation in this matter (Qadar) that caused the destruction of those who came before you! I am determined to not have you dispute amongst yourselves in this matter (of Qadar)." (Hadith)
"Discussion about Qadar has been left for the evil people among my Ummah (nation) to discuss." (Hadith)