Ubaydullah bin 'Abdullah bin 'Utba عبيد الله بن عبد الله بن عتبة بن مسعود · The Book of Oaths and Vows

"I heard the Messenger of Allah say: 'Whoever vows to obey Allah, let him obey Him, and whoever vows to disobey Allah, let him not disobey Him.'"

"The Messenger of Allah said: 'The best of you are my generation, then those who come after them, then those whom after them, then those who come after them.' -I do not know if he said two times after him or three. Then he mentioned some people who betray and cannot be trusted, who bear witness without being asked to do so, who make vows and do not fulfill them, and fatness will prevail among them."

"The Messenger of Allah passed by a man who was leading another man by a rope. The Prophet took it, and cut it, and he said: 'It is a vow.'"