Musannaf Ibn Abi Shayba 9:1643

Jarir narrated to us, from Mughira, from Abu Ma'shar, from Ibrahim, regarding a man who has multiple wives (co-wives): He said: They used to treat them equally until there remained a remainder of what was measured out of *sawiq* (barley meal) and food. Then they would divide it handful by handful when there remained something that could not be measured.