On minor oaths being of no consequence and not entailing expiation. That is what one says unintentionally like, "No, by Allah" and "Yes, by Allah."

Riyad as-Salihin (The Meadows of the Righteous)

by Imam Nawawi

317. Chapter: On minor oaths being of no consequence and not entailing expiation. That is what one says unintentionally like, "No, by Allah" and "Yes, by Allah."

Allah Almighty says, "Allah does not take you to task for your inadvertent oaths, but He will take you to task for oaths you make intentionally. The expiation in that case is to feed ten poor people with the average amount you feed your family, or to clothe them, or to free a slave. Anyone without the means to do so should fast three days. That is the expiation for breaking oaths when you have sworn them. Keep to your oaths." (W5:91; H5:89)

1719. 'A'isha said, "This ayat, 'Allah will not call you to account for what is futile in your oaths,' was sent down about when a man says, 'No, by Allah,' and 'Yes, by Allah.'"