Taking an oath on anyone besides Allah Ta'ala
Q: I just came to know yesterday that taking a qasam of ghairullah (anyone besides Allah) is not allowed in Islam.
I don't remember taking a qasam of ghairullah but I have a doubt that years ago I might have asked someone in texting to take a qasam of his mother and he refused to take it. I was ignorant about it. What should I do now?
Is asking someone to take qasam of his mother is also sin? although he refused to take it.