Musnad Ahmad 624:3

Yahya ibn Adam narrated to us, Sufyan narrated to us, from ‘Asim, from Zirr ibn Hubaysh, who said: I came to Safwan ibn ‘Assal al-Muradi and asked him about wiping over the leather socks (khuffayn). He said: "We used to be with the Messenger of Allah, may Allah bless him and grant him peace, and he would command us not to remove our leather socks for three days, except in the case of major ritual impurity (janabah), but not for defecation, urination, or sleep." Then a Bedouin with a loud voice came and said: "O Muhammad, a man loves a people but has not yet joined them." The Messenger of Allah, may Allah bless him and grant him peace, said: "A person is with those whom he loves."