Musannaf Ibn Abi Shayba 9:843

Ibn ‘Uyaynah narrated to us, from Ibn Abi Najih, from Mujahid, who said: "He shall not marry until the waiting period (*‘iddah*) of the woman he divorced has ended." ‘Ali said: "If there is no inheritance between them and there is no right of return (*raj‘ah*) upon her, then there is no harm in him marrying."