Ya'la bin Umayyah:
"I said to 'Umar [bin Al-Khattab]: 'Allah said: That you shorten the Salat if you fear and the people are safe (4:101).' So 'Umar said: 'I wondered about that just as you have wondered. So I mentioned that to the Messenger of Allah (ﷺ), and he said: "It is charity which Allah has given to you, so accept His charity."