Ṣaḥīḥ al-Bukhārī 5999

The full narration

Narrated `Umar bin Al-Khattab:Some Sabi (i.e. war prisoners, children and woman only) were brought before the Prophet (ﷺ) and behold, a woman amongst them was milking her breasts to feed and whenever she found a child amongst the captives, she took it over her chest and nursed it (she had lost her child but later she found him) the Prophet said to us, "Do you think that this lady can throw her son in the fire?" We replied, "No, if she has the power not to throw it (in the fire)." The Prophet (ﷺ) then said, "Allah is more merciful to His slaves than this lady to her son