It was the custom of the Arabs during the pre-Islamic period to swear by everything that was revered and considered good. Among such practices was their swearing by trustworthiness. It has been said that what is meant by "trustworthiness" here refers to acts of worship. The Prophet (peace and blessings of Allah be upon him) forbade swearing by it because oaths should only be made by Allah, and swearing by trustworthiness equates it with the essence of Allah. The Prophet's statement (peace and blessings of Allah be upon him) "is not one of us" means: he is not among the community of Muslims, or it means that he is not among those who follow our example, but rather is among those who imitate others, as this is characteristic of the People of the Book. All of this serves as a deterrent and stern warning against such oaths..