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

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.