Sufyan bin Sa‘id Ath-Thawri سفيان الثوري · The Chapters on Expiation

"I took an oath by Lat and 'Uzza. The Messenger of Allah (ﷺ) said : 'Say: "La ilaha illallah wahdahu la sharika lahu" (None has the right to be worshipped but Allah alone, with no partner or associate)," then spit toward your left three times, and seek refuge with Allah, and do not do that again."'

"Whoever swears an oath and says In sha' Allah, will never break his oath."

"Whoever makes a vow and does not state it specifically, the expiation (for such a vow) is the expiation for breaking an oath. Whoever makes a vow and is not able to fulfill it, the expiation for that is the expiation for breaking an oath. Whoever makes a vow and is able to fulfill it, let him do so."