Chapter on the Pardon for the Slip of the Tongue in Oaths: Allah the Exalted said

The reader: In the name of Allah, the Most Gracious, the Most Merciful.
Praise be to Allah, Lord of the worlds, and may peace and blessings be upon our Prophet Muhammad, and upon his family and all his Companions:
He said -may Allah have mercy on him-: “Chapter on the Pardon for the Slip of the Tongue in Oaths:
Allah the Exalted said:

Allah will not impose blame upon you for what is meaningless in your oaths, but He will impose blame upon you for [breaking] what you intended of oaths. So its expiation is the feeding of ten needy people from the average of that which you feed your [own] families or clothing them or the freeing of a slave. But whoever cannot find [or afford it] - then a fast of three days [is required]. That is the expiation for oaths when you have sworn. But guard your oaths

لا يؤاخذكم الله باللغو في أيمانكم ولكن يؤاخذكم بما عقَّدتم الأيمان فكفارته إطعام عشرة مساكين من أوسط ما تطعمون أهليكم أو كسوتهم أو تحرير رقبة * فمن لم يجد فصيام ثلاثة أيام ذلك كفارة أيمانكم إذا حلفتم واحفظوا أيمانكم

[Al-Ma'idah 5:89]

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Aisha (may Allah be pleased with her) said: أُنزلت هذه الآية : لا يؤاخذكم الله باللغو في أيمانكم في قول الرجل: لا والله، وبلى والله This verse was revealed: “Allah does not hold you accountable for the slip of the tongue in your oaths” regarding a man saying: “No, by Allah,” or “Yes, by Allah” Al-Bukhari narrated it.”

The Shaykh : In the name of Allah, the Most Gracious, the Most Merciful:
The author -may Allah have mercy on him- said in his book *Riyad al-Saliheen*: “Chapter on the Pardon for the Slip of the Tongue in Oaths”: The slip of the tongue in an oath is the oath that a person says on his tongue without intending it in his heart. Allah the Exalted has pardoned that because it often happens that a person says: “No, by Allah, I am not going,” or “No, by Allah, I am not coming,” or “No, by Allah, I am not doing it,” and the like. When this became common on the tongues of people, Allah pardoned it. Allah the Exalted said: : The Mother of the Believers, Aisha (may Allah be pleased with her), explained it as a man saying: “No, by Allah,” or “Yes, by Allah,” in the course of conversation without intending an oath. One is not held accountable for this, nor does one sin by it, nor does one break the oath, nor is expiation obligatory for it. However, if a person swears an oath with a firm resolve, saying: “By Allah, I will not do such and such,” or “By Allah, I will certainly do such and such,” and then does not do it, expiation becomes obligatory upon him. It is: freeing a slave, or feeding ten poor people, or clothing them. Allah the Exalted began with feeding because it is the easiest of the three. He said: : If he does not find [the means], then he fasts three consecutive days without breaking the fast in between. This is from the vastness of the mercy of Allah, Mighty and Majestic: that these oaths which are repeated on the tongues and not intended by the swearer carry no sin and no expiation, because that happens frequently.
But despite that, Allah, Mighty and Majestic, says: meaning: Do not multiply oaths, and do not neglect the expiation if you break them. Rather, keep them, because the oath is a matter of great gravity. For this reason, Allah the Exalted called its violation a breach, and indeed the Prophet (peace and blessings be upon him) called it a breach. For if it were not for the mercy of Allah, a person who swears would be bound to fulfill it. But from the grace of Allah is that He made it easy for a person to be able to go against what he swore to, provided it is not a sin. And success is from Allah.