All perfect praise be to Allah, The Lord of the Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all his family and companions.
Pleasing Allah then husband are among the characteristics of a righteous wife, so if he swears an oath concerning her she fulfills it. It was narrated from Abu Umamah that the Prophet (PBUH) used to say: “Nothing is of more benefit to the believer after Taqwa of Allah than a righteous wife whom, if he commands her she obeys him, if he looks at her he is pleased, if he swears an oath concerning her she fulfills it, and when he is away from her she is sincere towards him with regard to herself and his wealth.” {Ibn Majah}.
In principle, a wife should believe her husband and spare him taking oaths since the latter are usually taken to establish rights, to confirm that one is telling the truth, and to bring reconciliation amongst people. Basically, when a person swears by Allah, others should believe him out of reverence for Allah`s name.
In addition, a wife isn`t allowed to accuse her husband of lying without an evidence since doing so reflects lack of marital tact on her part. In principle, a Muslim should avoid swearing by Allah except before a judge, and it is prohibited that he swears by Allah falsely (intentionally) since a false oath dips its taker into Hellfire.
Al-Imam An-Nawawi (May Allah be pleased with him) said: "If he falsely swore by Allah (intentionally)about a past event then he has taken a false oath which dips him in sin or in Hellfire in addition to having committed one of the major sins. Therefore, he should expiate that oath." And Allah Knows Best.