Muwatta Malik #1493

Malik related to me from al-Ala ibn Abd ar-Rahman from Mabad ibn Kab as-Salami from his brother Abdullah ibn Kab ibn Malik al-Ansari from Abu Umama that the Messenger of Allah, may Allah bless him and grant him peace, said, "Whoever cuts off the right of a muslim man by his oath, Allah forbids him the Garden and obliges the Fire for him." They said, "Even if it is something insignificant, Messenger of Allah?" He said, "Even if it is a tooth-stick, even if it is a tooth- stick," repeating it three times.