Is the Hadith, "If someone swears by Allah, you must believe him, and if he is lying, that is on him, but we must believe him," authentic, and where can it be found?

Ibn Majah narrated from Ibn Umar that the Prophet, peace and blessings be upon him, said: "Do not swear by your fathers. Whoever swears by Allah, let him be truthful. Whoever is sworn to by Allah, let him be content. And whoever is not content with Allah, then he is not from Allah."

The meaning of the hadith (definition) is not that it is obligatory to believe everyone who swears by Allah, because the Sharia (definition) is built upon believing the truthful and disbelieving the liar. Interpretation of the hadith: 1. For the one swearing: He is commanded to be truthful in his oath. 2. For the one for whom the oath is sworn: He is commanded to be content with the oath of the one swearing, and this is if the one swearing is truthful. The oath increases its emphasis.

His saying: "And whoever is not content, then he is not from Allah" indicates that discontent is a major sin, but it must be noted that this is in the case where the one swearing is truthful. So, if the one swearing is not trustworthy or is definitively a liar, then there is no obligation to be content.

As for the one for whom the oath is sworn, he is not obliged to believe the one swearing in the following cases: If his falsehood is known. If his falsehood is more probable.

And he must believe him in the following cases: If both matters are equal (truthfulness and falsehood). If his truthfulness is more probable. If his truthfulness is known.

This is in sensory matters. As for matters of legal judgment, one must be content with the oath and abide by its requirements, because it is part of being content with the legal ruling, which is obligatory.