قَالَ مَالِك : أَحْسَنُ مَا سَمِعْتُ فِي هَذَا، أَنَّ اللَّغْوَ حَلِفُ الْإِنْسَانِ عَلَى الشَّيْءِ يَسْتَيْقِنُ أَنَّهُ كَذَلِكَ، ثُمَّ يُوجَدُ عَلَى غَيْرِ ذَلِكَ فَهُوَ اللَّغْوُ
Imam Malik, may Allah have mercy on him, said: There are three types of oaths:
One is the "idle oath" (laghw qasm): it is when a person swears an oath thinking something to be true, then it turns out to be otherwise.