A comparison he made using a woman in front of him
Prisoners were brought in, and a woman among them was searching for her child.
اللَّهُ أَرْحَمُ بِعِبَادِهِ مِنْ هَذِهِ بِوَلَدِهَا
He asked them: do you think this woman would throw her child into the fire? They said no, not if she could prevent it. He said: Allah is more merciful to His servants than this woman is to her child.
Where this comes from
She had found her baby among the captives, picked him up, held him to her chest and fed him. He pointed at her and asked the question.
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
Source
Ṣaḥīḥ al-Bukhārī · 5999
- Agreed upon as authentic (al-Bukhārī / Muslim)