Praise be to Allah.
This question is rather ambiguous but may be discussed as follows.
If he said, “By Allah, I will do such and such,” or “By Allah, I will help you to do such and such,” or “By Allah, he did not do such and such” -- and he did that for the purpose of reconciliation, then if he swore an oath for the purpose of reconciliation in a way that did not harm anyone, there is nothing wrong with it. [So he could say:] “By Allah, So and so said such and such about you… By Allah, such and such a group praised you and thanked you and say that you are their friend,” in order to bring about reconciliation between them.
But if he said, “By Allah, I will visit you, or I will help you with something if you reconcile, and stop this dispute,” then in this case he has to fulfil what he promised them, because promises are important and one of the characteristics of the believer is that he fulfils his promises. Allah said concerning Ismaa‘eel (interpretation of the meaning):
“And mention in the Book (the Qur’ân) Ismâ‘îl (Ishmael). Verily, he was true to what he promised, and he was a Messenger, (and) a Prophet”
He should not break his promise, because breaking a promise is one of the characteristics of the hypocrites, and when a hypocrite makes a promise, he breaks it. He has to offer expiation if he did break his promise, even though he acquired one of the characteristics of the hypocrites by breaking his promise. He still has to offer kafaarat yameen (expiation for breaking an oath), because he said, “By Allah, I will visit you on such and such a day,” or “By Allaah, I will help you,” but he did not do that, so he has to face the consequences and he may be sinning according to those who say that it is obligatory to fulfil oaths based on the apparent meaning of the evidence. Or he may not be sinning, but he has acquired one of the characteristics of the hypocrites that he should not have acquired.
The apparent meaning of the shar‘i evidence is that fulfilling promises is something obligatory, and that breaking them is something haraam and is one of the characteristics of the hypocrites. It is not appropriate for one who seeks to bring about reconciliation to break his promise, because this will affect future attempts at reconciliation. So he should never break his promise; rather he should keep his promise and strive hard to do that.
This also applies to other oaths that are sworn falsely in order to bring about reconciliation and which do not harm anyone. There is nothing wrong with doing that for this purpose of reconciliation, because of the apparent meaning of the saheeh hadeeth narrated from Umm Kulthoom bint ‘Uqbah ibn Abi Ma‘eet who said: I heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “He is not a liar who reconciles between people and conveys something good or says something good.” She said: I never heard him allowing a concession for any kind of lying except in three cases: when reconciling between people, during war, and when a man speaks to his wife or a woman speaks to her husband.
Lying which does not harm people is permissible in cases of reconciliation, but it should benefit the people among whom reconciliation is sought, and it should not harm anyone else. End quote.
Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him)