Musannaf Ibn Abi Shayba 9:779

Shababa narrated to us, from Warqa’, from Ibn Abi Najih, from Mujahid regarding [the verse]: "Then approach them from where Allah has ordained for you." He said: They were commanded to abstain from women during menstruation, and to approach them from where Allah has ordained for you when they have become pure, from the place where they were forbidden during their menstruation.