Musnad Ahmad 196
It was narrated from 'Umar that he said to the Prophet ﷺ:
What do you think about what we are striving for is it something already decided or something that is evolving now or something new? He said: “It is something already decided,` `Umar said: Then why don't we rely on what is already decided? He said: `Strive, O son of al-Khattab, for everyone will be helped; whoever is one of the people of bliss will strive for that bliss and whoever is one of the people of doom will strive for that doom.”
حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، حَدَّثَنَا شُعْبَةُ، وَحَجَّاجٌ، قَالَ سَمِعْتُ شُعْبَةَ، عَنْ عَاصِمِ بْنِ عُبَيْدِ اللَّهِ، عَنْ سَالِمٍ، عَنِ ابْنِ عُمَرَ، عَنْ عُمَرَ، رَضِيَ اللَّهُ عَنْهُمَا أَنَّهُ قَالَ لِلنَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَرَأَيْتَ مَا نَعْمَلُ فِيهِ أَقَدْ فُرِغَ مِنْهُ أَوْ فِي شَيْءٍ مُبْتَدَإٍ أَوْ أَمْرٍ مُبْتَدَعٍ قَالَ فِيمَا قَدْ فُرِغَ مِنْهُ فَقَالَ عُمَرُ أَلَا نَتَّكِلُ فَقَالَ اعْمَلْ يَا ابْنَ الْخَطَّابِ فَكُلٌّ مُيَسَّرٌ أَمَّا مَنْ كَانَ مِنْ أَهْلِ السَّعَادَةِ فَيَعْمَلُ لِلسَّعَادَةِ وَأَمَّا أَهْلُ الشَّقَاءِ فَيَعْمَلُ لِلشَّقَاءِ‏.‏