What is fate?
Whatever happens in the world and whatever people do, whether good or bad, everything happens as per the eternal knowledge of Almighty Allah. Whatever is going to happen is in the knowledge of Allah عَزَّوَجَلَّ and is already with him in written form. (Kitab-ul-Aqaaid, pp. 24)
Evidence of fate
Evidence of fate is present in the Holy Quran and blessed Ahadees as it has been stated in this blessed Ayah:
اِنَّا كُلَّ شَیْءٍ خَلَقْنٰهُ بِقَدَرٍ(۴۹)
We have indeed created everything with a proper measure.
[Kanz-ul-Iman (translation of Quran)](Part 27, Surah Al-Qamar, Ayah 49)
The Beloved Prophet صَلَّى اللّٰـە عَلَيْهِ وَاٰلِهٖ وَسَلَّم has stated six things while answering to a question about faith.
Having faith in (1) Allah Almighty (2) Angels (3) Heavenly revealed books (4) Prophets (5) the Judgement Day (6) Fate, whether good or bad, it is from Allah عَزَّوَجَلَّ. (Muslim, pp. 33, Hadees 93)
Ruling on the denial of fate
Denying fate is Kufr [disbelief]. (Minh-ur-Raud-ul-Azhar, pp. 69) The Beloved Prophet صَلَّى اللّٰـە عَلَيْهِ وَاٰلِهٖ وَسَلَّم has declared those who deny fate to be the fire worshippers of this Ummah. (Abu Dawood, vol. 4, pp. 294, Hadees 4691)
It is forbidden to have a debate about fate
Remember! The belief in fate is extremely delicate and complex in Islamic beliefs. It is forbidden to have a debate about fate and ask questions with how and why. It is stated in Tirmizi Sharif that Sayyiduna Abu Hurayrah رَضِىَ اللّٰـەُ عَـنْهُ said: The Beloved Prophet صَلَّى اللّٰـە عَلَيْهِ وَاٰلِهٖ وَسَلَّم came to us while we were having a debate over the matter of fate. He صَلَّى اللّٰـە عَلَيْهِ وَاٰلِهٖ وَسَلَّم got upset, even his blessed face turned red as if pomegranates were squeezed on his blessed cheeks and said: Have you been given permission to do this or have I been sent to you with this? When the people before you disputed this matter, they were killed. I make it mandatory for you not to dispute this matter. (Tirmizi, vol. 4, pp. 51, Hadees 2140)
Benefits of having faith in fate
1. The person who has faith in fate remains patient when he is in trouble and suffering from a disease and stays safe from Haraam acts like suicide because their occurrence is in accordance with the fate and is a test.
2. He agrees on the distribution made by Allah عَزَّوَجَلَّ and His will.
3. He does not feel guilt over the frustrations he experienced in the past, does not worry about the present condition and has no fear of the future.
4. He loves the Creator instead of creation.
5. Faith in fate is the best treatment of ‘jealousy.’
May Allah عَزَّوَجَلَّ give us Taufeeq to follow the right beliefs of Ahl-e-Sunnat-o-Jama’at throughout our life and also bless us with the death having the same beliefs. اٰمِیْن بِجَاہِ النَّبِیِّ الْاَمِیْن صلَّی اللہ علیہ واٰلہٖ وسلَّم
 The knowledge of the Almighty which exists for ever.