Hadith: There is none among you except that his seat in Paradise or in Hell is decreed

عن علي رضي الله عنه قال: كُنَّا في جَنَازة في بَقِيعِ الغَرْقَدِ، فَأتَانَا رسول الله صلى الله عليه وسلم فَقَعَدَ، وَقَعَدْنَا حَوْلَه ومعه مِخْصَرَةٌ فَنَكَّسَ وجعل يَنْكُتُ بِمِخْصَرَتِهِ، ثم قال: «ما مِنْكُمْ من أحَدٍ إلا وقد كُتِبَ مَقْعَدُه من النَّار ومَقْعَدُه من الجنَّة» فقالوا: يا رسول الله، أفلا نَتَّكِلُ على كِتَابِنَا؟ فقال: «اعملوا؛ فَكلٌّ مُيَسَّرٌ لما خُلِقَ له...» وذكر تمام الحديث.
[صحيح] - [متفق عليه]

‘Ali (may Allah be pleased with him) reported: "We were attending a funeral at Baqī‘ aI-Gharqad (Muslim cemetery in Madīnah). The Messenger of Allah (may Allah's peace and blessings be upon him) came to us and sat down, and we sat down around him. He had a small stick in his hand. He lowered his head and started scraping the ground with the stick, then said: "There is none among you, except that his seat in Paradise or in Hell is decreed." They said: "O Messenger of Allah, should we depend on what has been decreed for us?" The Prophet (may Allah's peace and blessings be upon him) said: "Exert the effort, for everyone will find it easy to do such deeds that will lead him to what he was created for..." Then he mentioned the rest of the Hadīth.
[Authentic hadith] - [Narrated by Bukhari & Muslim]

Explanation

The Companions (may Allah be pleased with him) were attending the funeral of one of them in the cemetery of the people of Madīnah. The Prophet (may Allah's peace and blessings be upon him) sat among them with a stick in his hand. He lowered his head towards the ground, as if he was thinking deeply and greatly concerned about something. He started to scratch the ground with the stick, then said that Allah, the Almighty, has decreed the fates of people and determined their seats in Paradise and Hell. When the Companions heard that, they said: If the fate of those who will be wretched and those who will be prosperous, those who will be in Paradise and those who will be in Hell, has already been predetermined and decreed, why should we not give up doing good deeds; for exerting effort is useless, given the fact that everything is decreed and predestined? The Prophet (may Allah's peace and blessings be upon him) answered that they should work hard and not rely upon the good and evil which Allah has predestined. Instead, they have to do what they are commanded to do, and refrain from what they are forbidden from doing. Indeed, Paradise and Hell are attained by people's deeds; those who do the deeds of the people of Paradise shall enter Paradise, and those who do the deeds of the people of Hell shall enter Hell. Everyone will find it easy to do such deeds that lead him to what he was created for, be it good or evil. Therefore, whoever is decreed to be among the prosperous, Allah will lead him to do the deeds of the prosperous, and whoever is decreed to be among the wretched, Allah will lead him to do the deeds of the wretched.