صحيح البخاري

Narrated Usama bin Zaid:

We were with the Prophet (ﷺ) when suddenly there came to him a messenger from one of his daughters who was asking him to come and see her son who was dying. The Prophet (ﷺ) said (to the messenger), "Go back and tell her that whatever Allah takes is His, and whatever He gives is His, and everything with Him has a limited fixed term (in this world). So order her to be patient and hope for Allah's reward." But she sent the messenger to the Prophet (ﷺ) again, swearing that he should come to her. So the Prophet got up, and so did Sa`d bin 'Ubada and Mu`adh bin Jabal (and went to her). When the child was brought to the Prophet (ﷺ) his breath was disturbed in his chest as if it were in a water skin. On that the eyes of the Prophet (ﷺ) became flooded with tears, whereupon Sa`d said to him, "O Allah's Messenger! What is this?" The Prophet (ﷺ) said, "This is mercy which Allah has put in the heart of His slaves, and Allah bestows His mercy only on those of His slaves who are merciful (to others)."