كتاب المقدمات
1
The Book of Miscellany
'Umar bin Al-Khattab (May Allah be pleased with him) reported:
Some prisoners were brought to Messenger of Allah (ﷺ) amongst whom there was a woman who was running (searching for her child). When she saw a child among the captives, she took hold of it, pressed it against her belly and gave it a suck. Messenger of Allah (ﷺ) said, "Do you think this woman would ever throw her child in fire?" We said, "By Allah, she would never throw the child in fire." Thereupon Messenger of Allah (ﷺ) said, "Allah is more kind to his slave than this woman is to her child".

[Al-Bukhari and Muslim].

وعن عمر بن الخطاب، رضي الله عنه ، قال‏:‏ قدم رسول الله ، صلى الله عليه وسلم، بسبي، فإذا امرأة من السبي تسعى، إذ وجدت صبياً في السبي أخذته، فألزقته ببطنها، فأرضعته، فقال رسول الله، صلى الله عليه وسلم‏:‏ “أترون هذه المرأة طارحة ولدها في النار‏؟‏” قلنا لا والله ‏.‏ قال‏:‏ ‏ "‏لله أرحم بعباده من هذه الأم بولدها‏"‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏
Arabic/English book reference : Book 1, Hadith 418