He is advised and told: You should not swear too much, even if you are truthful, because God Almighty says, “And guard your oaths” [al-Maa’idah: 89], and His saying, peace be upon him: There are three whom God will not speak to, nor look at on the Day of Resurrection, nor purify them, and they will have a painful punishment: an adulterer, an arrogant breadwinner, and a man who makes God does not buy his merchandise except with his right hand and does not sell except with his right hand.
The Arabs praised the lack of faith, as the poet said:
And the mechanism: it is the right.
It is legitimate for the believer to reduce the oath, even if it is sincere. Because more of them may make him lie.
It is known that lying is forbidden, and if it is with the oath, it becomes even more forbidden. When it was proven on the authority of the Prophet, peace be upon him, from the hadith of Umm Kulthum bint Uqba bin Abi Muait, may God be pleased with her, that the Prophet, peace be upon him, said: He is not a liar who reconciles between people and says good or develops good. Reconciliation between people, war, the man’s conversation with his wife, and the woman’s conversation with her husband. Narrated by Muslim in the Sahih.
So if he says about reconciliation between people: By Allah, your companions love reconciliation and they love that the word agrees, and they want such and such, then he comes to others and says the same to them, and his intention is goodness and reform, then there is nothing wrong with that because of the hadith mentioned.
Likewise, if he sees a person who wants to kill someone unjustly or to wrong him in something else, and he says to him: By God, he is my brother, so that he can rid him of this oppressor if he wants to kill him unjustly or beat him unjustly, and he knows that if he says: my brother, he will leave him out of respect for him. He must do something like this in order to rid his brother of injustice.
What is meant is that the basic principle regarding false oaths is that they are forbidden and prohibited, unless they result in a greater interest greater than lying, as in the three mentioned in the previous hadith [1].
Total Fatwas of Ibn Baz (1/ 54).