Abdullah bin Abi Qatadah narrates from his father, Sayyiduna Abu Qatadah (may Allah be pleased with him), that the Messenger of Allah (peace and blessings be upon him) said: "I stand for the prayer intending to make it long, then I hear the crying of a child, so I shorten the prayer, not wanting to make things hard for his mother."
In the narration of al-Adib it is: "I shorten my prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5280
Sayyiduna Anas (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him): "I begin the prayer intending to make it long, but on hearing the crying of a child I shorten the prayer, so that the child's mother does not remain in distress because of his crying."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5281