The Messenger of Allah ﷺ set the period of postnatal bleeding at forty days, unless a woman sees purity before that.
حدثنا عبد الله بن سعيد حدثنا المحاربي عن سلام بن سليم أو سلم شك أبو الحسن وأظنه هو أبو الأحوص عن حميد
كان رسول الله ﷺ وقت للنفساء أربعين يوما إلا أن ترى الطهر قبل ذلك
No references are available.
[Its chain of transmission is daif] and Busiri graded it sahih. Muharibi used to practice tadlis and narrated using "an," and Sallam is al-Tawil as Bayhaqi said, 1/343, and he is discarded as stated in al-Taqrib and elsewhere. The hadith has many corroborating narrations.