Hadith: Verily, I would stand up for prayer intending to prolong it, but I hear the crying of an infant, so I shorten my prayer lest I make it burdensome for his mother

عن أبي قتادة وأنس بن مالك رضي الله عنهما مرفوعاً: «إني لأقوم إلى الصلاة، وأريد أن أُطَوِّلَ فيها، فأسمع بكاء الصبي فأَتَجَوَّزُ في صلاتي كراهيةَ أن أَشُقَّ على أمه».
[صحيح] - [حديث أبي قتادة -رضي الله عنه-: رواه البخاري. حديث أنس -رضي الله عنه-: متفق عليه]

Abu Qatādah and Anas ibn Mālik (may Allah be pleased with both of them) reported that the Prophet (may Allah's peace and blessings be upon him) said: "Verily, I would stand up for (congregational) prayer intending to prolong it, but I hear the crying of an infant, so I shorten my prayer lest I make it burdensome for his mother."
[Authentic hadith] - [Narrated by Bukhari - Narrated by Bukhari & Muslim]

Explanation

The Prophet (may Allah's peace and blessings be upon him) would start leading a congregational prayer intending to make the prayer long. However, if he heard an infant crying, he would shorten the prayer so that it would not be hard on the infant's mothers, since her heart would be distracted by the crying of her child.