Abu Qatada al-Harith ibn Rib'i reported that the Prophet, may Allah bless him and grant him peace, said, "I stand in prayer and would like to make it long but I hear the crying of a child and shorten my prayer not wanting to make things difficult for its mother."

Riyadh-as-Saliheen by Imam Al-Nawawi, volume 2, hadith number 231 - Sunni Hadith