The Quran

لا يُؤاخِذُكُمُ اللَّهُ بِاللَّغوِ في أَيمانِكُم وَلٰكِن يُؤاخِذُكُم بِما عَقَّدتُمُ الأَيمانَ ۖ فَكَفّارَتُهُ إِطعامُ عَشَرَةِ مَساكينَ مِن أَوسَطِ ما تُطعِمونَ أَهليكُم أَو كِسوَتُهُم أَو تَحريرُ رَقَبَةٍ ۖ فَمَن لَم يَجِد فَصِيامُ ثَلاثَةِ أَيّامٍ ۚ ذٰلِكَ كَفّارَةُ أَيمانِكُم إِذا حَلَفتُم ۚ وَاحفَظوا أَيمانَكُم ۚ كَذٰلِكَ يُبَيِّنُ اللَّهُ لَكُم آياتِهِ لَعَلَّكُم تَشكُرونَ

(Saheeh International)

Allāh will not impose blame upon you for what is meaningless¹ in your oaths, but He will impose blame upon you for [breaking] what you intended of oaths. So its expiation² 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.³ Thus does Allāh make clear to you His verses [i.e., revealed law] that you may be grateful.

i.e., what is sworn to only out of habit of speech or what one utters carelessly without true intent.
i.e., that for a deliberate oath.
i.e., do not take oaths indiscriminately or swear to do that which is sinful, requiring expiation.