Musnad Abu Ya'la al-Mawsili 115:303

Ubayd Allah narrated to us, Khalid ibn al-Harith narrated to us, Sa'id narrated to us, from Qatadah, from Anas, from the Prophet, who said: "Indeed, I enter into the prayer and I intend to prolong it, but then I hear the crying of a child, so I shorten my prayer due to what I know of the intensity of his mother's distress because of that."