Musannaf Ibn Abi Shayba 1:846

Yazid narrated to us, from Habib, from ‘Amr ibn Haram, who said: Jabir ibn Zayd was asked about a woman who becomes in a state of major ritual impurity (janaba), then menstruates before she performs ghusl. He said: Even if she menstruates, it is an obligation upon her to perform ghusl.