al-Bukhari.

6/593 – Al-Hasan ibn ʿAlī (may Allah be pleased with them both) said, “I memorized from the Messenger of Allah (peace and blessings be upon him): ‘Leave what makes you doubt for what does not make you doubt.’” Related by al-Tirmidhi, who declared it a sound, authentic hadith.

[Commentary]

The compiler—may Allah have mercy on him—cites these two hadiths in the chapter on scrupulous piety and avoiding doubtful matters in Riyad al-Salihin. The first, the hadith of ʿUqbah, concerns the rules of breastfeeding; the second, the hadith of al-Hasan ibn ʿAlī ibn Abi Talib, concerns abstaining from what is ambiguous.

Regarding the first: ʿUqbah married the daughter of Ibn Abi Ihab. After the marriage a woman came forward and said, “I nursed both him and the woman he has just married,” meaning that he is her foster brother through breastfeeding. A foster brother is forbidden to her just as a blood brother is, for the Prophet (peace and blessings be upon him) said, “Breastfeeding makes unlawful what lineage makes unlawful.” Certain conditions, however, must be met.

The first condition is that the milk be human. If two infants were to share milk from a ewe, a cow, or a she-camel, they would not become foster siblings, because it is essential that