Musnad Ahmad 30:1651

Mu'awiyah ibn 'Amr narrated to us, he said: Za'idah narrated to us, from 'Abd al-Malik ibn 'Umayr, from Abu al-Awbar, he said: A man came to Abu Hurayrah and said: "Are you the one who forbids people from praying while wearing their sandals?" He said: "No, but by the Lord of this Sanctuary, I indeed saw the Messenger of Allah, peace and blessings of Allah be upon him, praying toward this station while wearing his sandals, and he departed while they were upon him." And the Prophet, peace and blessings of Allah be upon him, forbade fasting on the day of Friday, unless it is during [a sequence of] days.