"The Messenger of Allah said: 'Do not swear by your fathers, nor by your mothers nor by the idols. Swear only by Allah, and do not swear unless you are sincere.'"
Sunan an-Nasa'i Book 35, Hadith 9
← Previous Hadith "The Messenger of Allah said: 'Allah forbids you to swear by your forefathers.'" 'Umar said: "By Allah, I never swore by them again, whether saying it for myself or reporting it of others."

Sunan an-Nasa'i Book 35, Hadith 8 Next Hadith → "The Messenger of Allah said: 'Whoever swears by a religion other than Islam, telling a lie, will be as he said.'" In his narration, Qutaibah said: "Intentionally." Yazid said: "Telling a lie will be as he said, and whoever kills himself with something. Allah will punish him with it in the Fire of Hell."

Sunan an-Nasa'i Book 35, Hadith 10