Musannaf Ibn Abi Shayba 3:6487

Abu Bakr narrated to us, he said: Mu'tamir ibn Sulayman narrated to us, from his father, who said: I asked Ibn Sirin about a woman whose menstrual period is for known days, then it increases beyond that. He said: "Women are more knowledgeable about that." He said: And I asked Qatadah, and I said: "A woman menstruates for known days, then it increases beyond five days?" He said: "She prays." I said: "Then four days?" He said: "She prays." I said: "Then three days?" He said: "She prays." I said: "Then two days?" He said: "That is from her menstruation." And I saw that he said it based on his own opinion.