Musnad Ahmad 1156:174

Isma'il narrated to us, he said: Hisham al-Dastawa'i narrated to us, from Yahya ibn Abi Kathir, from Abu Salamah, from Zaynab bint Umm Salamah, from Umm Salamah: "That the Prophet of Allah, peace and blessings of Allah be upon him, used to kiss her while he was fasting, and they used to perform ghusl (ritual bathing) from a single vessel."