Musnad Abu Ya'la al-Mawsili 119:3

Muhammad ibn Abdullah ibn Numayr narrated to us, Anas ibn Iyad narrated to us, from Sharik ibn Abi Namir, who said: I heard Anas saying: The Messenger of Allah (peace and blessings of Allah be upon him) would hear the crying of a child behind him, so he would shorten [the prayer] for fear that his mother might be distracted.