Musnad Ahmad 174
It was narrated that Ya'la bin Umayyah said:
I said to 'Umar bin al Khattab رضي الله عنه , `And when you (Muslims) travel in

the land, there is no sin on you if you shorten As­Salah (the prayer) if you fear that the disbelievers may put you in 

trial (attack you)` (al Nisa' 4:101]. But now the people are safe. He said: I wondered the same thing as you are 

wondering, and I asked the Messenger of Allah ﷺ about that. He said: “It is a charity that Allah has bestowed upon 

you, so accept His charity.`
حَدَّثَنَا ابْنُ إِدْرِيسَ، أَنْبَأَنَا ابْنُ جُرَيْجٍ، عَنِ ابْنِ أَبِي عَمَّارٍ، عَنْ عَبْدِ اللَّهِ بْنِ بَابَيْهِ، عَنْ يَعْلَى بْنِ أُمَيَّةَ، قَالَ سَأَلْتُ عُمَرَ بْنَ الْخَطَّابِ قُلْتُ ‏{‏لَيْسَ عَلَيْكُمْ جُنَاحٌ أَنْ تَقْصُرُوا مِنْ الصَّلَاةِ إِنْ خِفْتُمْ أَنْ يَفْتِنَكُمْ الَّذِينَ كَفَرُوا‏}‏ وَقَدْ أَمَّنَ اللَّهُ النَّاسَ فَقَالَ لِي عُمَرُ عَجِبْتُ مِمَّا عَجِبْتَ مِنْهُ فَسَأَلْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَنْ ذَلِكَ فَقَالَ صَدَقَةٌ تَصَدَّقَ اللَّهُ بِهَا عَلَيْكُمْ فَاقْبَلُوا صَدَقَتَهُ‏.‏