Musnad Ahmad 2:163

Yahya narrated to us, from Ibn Jurayj, Abd al-Rahman ibn Abd Allah ibn Abi Ammar narrated to me, from Abd Allah ibn Babiyah, from Ya'la ibn Umayyah, who said: I said to Umar ibn al-Khattab: "The people shorten the prayer today, yet Allah, the Mighty and Majestic, only said: 'If you fear that those who disbelieve may afflict you' [An-Nisa: 101], and that day has passed!" He said: "I wondered about what you wondered about, so I mentioned that to the Messenger of Allah, peace and blessings of Allah be upon him. He said: 'It is a charity that Allah has bestowed upon you, so accept His charity.'"