Musnad Ahmad 1153:695

Hassan narrated to us, he said: Shayban narrated to us, from Yahya, he said: Muhammad ibn Abd al-Rahman ibn Thawban informed me, that Aisha, the Mother of the Believers, said: The Messenger of Allah, may Allah bless him and grant him peace, said: "That which is forbidden by reason of nursing is that which is forbidden by reason of lineage: whether it be a maternal uncle, or a paternal uncle, or a brother's son."