Riyad as-Salihin (The Meadows of the Righteous)
by Imam Nawawi
1649. Abu Hurayra reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "None of you should walk wearing only one sandal. You should wear both of them or leave both of them off." [Agreed upon]
In one variant, "Or take them both off."
1650. Abu Hurayra said, "I heard the Messenger of Allah, may Allah bless him and grant him peace, say, 'When the strap of the sandal of one of you breaks, he should not walk wearing the other until he has mended it.'" [Muslim]