Narrated Abdullah ibn Umar: When we were with the Prophet (peace be upon him) on one of his expeditions he came upon some people and asked who they were, to which they replied that they were Muslims. A woman who had a son of hers with her was kindling a fire under her pot, and when the heat increased she moved him away. She then went to the Prophet (peace be upon him) and asked, “You for whom I would give my father and mother as ransom, tell me if Allah is not the Most Merciful of those who are merciful.” He replied that He certainly was. She asked, “Is Allah not More Merciful to His servants than a mother to her child?” and when he assured her that He certainly was, she replied that a mother does not cast her child into the fire. Allah’s Messenger (peace be upon him) then bowed his head and wept, and afterwards raised it, looked at her and said, “Allah punishes only those of His servants who act audaciously towards Him and refuse to say that there is no god but Allah.”

IbnMajah transmitted it.

Al-Tirmidhi – Hadith 756