Question: I had a discussion with a Muslim brother concerning the impermissibility of swearing by other than Allaah.
In this discussion I told him that based on what I have studied, swearing by other than Allaah is Shirk Asghar (minor form of associating others in worship with Allaah), as Shaykh Muhammad ibn ‘Abdul-Wahhaab explained it in his book: Al-Shirk Al-Asghar is to swear by other than Allaah, such as when a person says, ‘I have none except Allaah and you’, or ‘I put my trust in Allaah and you’ …Etc. However, he said: It is permissible to swear by the Qur’aan because it is one of Allaah’s Attributes. There are numerous opinions held by some practitioners of Ijtihaad (juristic effort to infer expert legal rulings) supporting his view. We would like the Committee to issue a Fatwa regarding this matter, for we know that they depend on the Saheeh Hadeeth (a Hadeeth that has been transmitted by people known for their uprightness and exactitude; free from eccentricity and blemish), may Allaah reward you!
Answer: As to swearing by any other than Allaah, such as saying: “What Allaah wills and you will”, “I have none except Allaah and you” and so on: if the people who make such oaths glorify in their hearts the creatures that they swear by the same as they glorify Allaah, this is Shirk Akbar (major form of associating others in worship with Allaah)… read more here.