Musnad Ahmad 1007:86

Ahmad ibn al-Hajjaj narrated to us, Abdullah ibn al-Mubarak informed us, al-Awza'i narrated to me, Yahya ibn Abi Kathir narrated to me, from Abdullah ibn Abi Qatadah, from his father, from the Prophet, peace and blessings of Allah be upon him, who said: "Indeed, I stand in prayer intending to prolong it, then I hear the crying of a child, so I shorten my prayer, disliking to cause hardship to his mother."