Sayyiduna Uthman bin Abi al-As al-Thaqafi (may Allah be pleased with him) said: Women in nifas will wait forty days, then perform ghusl.
Marfu' hadiths (attributed to the Prophet) have also been narrated on this; apart from what we have mentioned, all of them are weak.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1611