It is narrated from the Mother of the Believers, Sayyidah Aishah, and the Mother of the Believers, Sayyidah Umm Salamah (may Allah be pleased with them both), that "the Messenger of Allah (peace and blessings be upon him) would be in a state of janabah (major ritual impurity) (at the time of Fajr), and then he (peace and blessings be upon him) would fast."
No one narrated this hadith from Irak bin Malik except Ja'far bin Rabi'ah.