Narrated Ya'la b. Umayyah: I remarked to 'Umar al-Khattab: Have you seen the shortening of the prayer by the people today while Allah has said: "If you fear that those who are infidels may afflict you", whereas those days are gone now? He replied: I have wondered about the same matter for which you wondered. So I mentioned this to the Messenger of Allah (ﷺ). He said: It is an act of charity which Allah has done to you, so accept his charity.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا أَحْمَدُ بْنُ حَنْبَلٍ، وَمُسَدَّدٌ، قَالاَ حَدَّثَنَا يَحْيَى، عَنِ ابْنِ جُرَيْجٍ، ح وَحَدَّثَنَا خُشَيْشٌ، - يَعْنِي ابْنَ أَصْرَمَ - حَدَّثَنَا عَبْدُ الرَّزَّاقِ، عَنِ ابْنِ جُرَيْجٍ، قَالَ حَدَّثَنِي عَبْدُ الرَّحْمَنِ بْنُ عَبْدِ اللَّهِ بْنِ أَبِي عَمَّارٍ، عَنْ عَبْدِ اللَّهِ بْنِ بَابَيْهِ، عَنْ يَعْلَى بْنِ أُمَيَّةَ، قَالَ قُلْتُ لِعُمَرَ بْنِ الْخَطَّابِ أَرَأَيْتَ إِقْصَارَ النَّاسِ الصَّلاَةَ وَإِنَّمَا قَالَ تَعَالَى { إِنْ خِفْتُمْ أَنْ يَفْتِنَكُمُ الَّذِينَ كَفَرُوا } فَقَدْ ذَهَبَ ذَلِكَ الْيَوْمُ . فَقَالَ عَجِبْتُ مِمَّا عَجِبْتَ مِنْهُ فَذَكَرْتُ ذَلِكَ لِرَسُولِ اللَّهِ صلى الله عليه وسلم فَقَالَ " صَدَقَةٌ تَصَدَّقَ اللَّهُ بِهَا عَلَيْكُمْ فَاقْبَلُوا صَدَقَتَهُ " .
sunnah.com