If fulfilling a vow becomes difficult for a man, let him expiate as for an oath

It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that a man came to the Prophet (peace and blessings be upon him) and said: My sister has vowed to walk to the House of Allah, and walking is very hard for her. He (peace and blessings be upon him) said: "Tell her to ride, since she is not able to walk; Allah has no need of your sister putting herself to hardship."
This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.

Sayyiduna Ibn Abbas (may Allah be pleased with them both) said, concerning a man who vows to walk but becomes unable and rides: He should perform Hajj again the following year, and (by way of making up for it) walk the part of the route he had ridden last time, and ride where he had walked.

It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that a man came to the Prophet (peace and blessings be upon him) and said: My sister has vowed to walk to the House of Allah. He (peace and blessings be upon him) said: "Indeed, Allah Almighty gains nothing from putting your sister to hardship. Tell her to perform Hajj riding and to give the expiation for her oath."
This hadith is sahih (authentic) on the condition of Imam Muslim, but the two Shaykhs (Bukhari and Muslim) did not record it.

It is narrated from Sayyidah Aishah (may Allah be pleased with her) that some meat was given to me as a gift, and the Messenger of Allah (peace and blessings be upon him) instructed me to send some of it to (Sayyidah) Zaynab (may Allah be pleased with her). I sent it, but she returned it. He (peace and blessings be upon him) said: "Send her more." I sent it again, but she returned it again. He (peace and blessings be upon him) said: "I adjure you to send her more." I sent it again, but she returned it again. Aishah (may Allah be pleased with her) says: Jealousy came over me and I said: She has rejected your word. He (peace and blessings be upon him) said: "You and she are far too insignificant before Allah for any of you to be guilty of disrespect towards me. I swear that I will not come to you for a month." So he (peace and blessings be upon him) stayed away from us for twenty-nine days and came to us on the evening of the thirtieth day. Aishah (may Allah be pleased with her) said: You had sworn not to come for a month? He (peace and blessings be upon him) said: "A month is like this, and also like this," and with a gesture of both his palms he (peace and blessings be upon him) made clear that a month can also be of 29 days.
This hadith is sahih (authentic) on the condition of Imam Bukhari, but the two Shaykhs (Bukhari and Muslim) did not record it; it also establishes that saying "I adjure you" falls under the ruling of an oath.

It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever swears an oath and then says 'In sha' Allah (if Allah wills)', he has the exception (from the oath becoming binding)."
This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it with this wording.

It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that when a man swears an oath, he has the right to say 'In sha' Allah' (if Allah wills) even if it is a year later, and it was concerning this that this verse was revealed: "And remember your Lord when you forget" [Surah al-Kahf: 24], meaning that when he remembers, he should make the exception (say In sha' Allah). Ali bin Mushir said: And al-A'mash used to act upon this.
This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it.