Majma al-Zawaid — Hadith 1536

Sayyiduna Abdullah bin Amr (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "The menstruating woman will watch for up to ten days. If she sees purity, she becomes pure; and if it exceeds ten days, she will be counted as a woman with istihadah (irregular bleeding): she will take the ritual bath (ghusl) and pray. If the blood flows heavily, she will put cotton in place, bind a cloth, and perform ablution (wudu) for every prayer. The woman in postnatal bleeding (nifas) will wait for up to forty days. Then, if she sees purity before that, she is counted as pure; and if it exceeds forty days, she takes the ruling of a woman with istihadah: she will take the ritual bath and pray. If the blood flows heavily, she will put cotton in place, bind a cloth, and perform ablution for every prayer."
Imam al-Tabarani recorded it in al-Mu'jam al-Awsat; its chain contains a narrator, Umar bin al-Husayn, who is da'if (weak).