Musannaf Ibn Abi Shaybah

Hazrat Ikrimah (may Allah have mercy on him) says that the waiting period (‘iddah) of a woman experiencing istihada (irregular bleeding) and a woman whose menstruation has no fixed pattern (sometimes occurring twice in a month and sometimes once in several months) is three months. Hazrat Qatadah (may Allah have mercy on him) also used to say the same.