What is the ruling on swearing by Allah?

This phrase can carry two meanings:

1. To make Allah swear (Istihlaf): This means asking Allah to swear an oath, which is impermissible. Allah is not to be asked to swear, for nothing is obligatory upon Him. And if He swears an oath, exalted be He, it is an oath initiated by Him. Muslim reported in a Hadith: "Indeed, I did not make you swear out of suspicion towards you, but Jibreel came to me and informed me that Allah, the Mighty and Exalted, boasts about you to the angels."

2. To swear by Allah (Al-Iqsam 'ala Allah): Permissible: That which stems from trust in Allah, strength of faith, good assumptions, and true reliance, as in the Hadith: "Perhaps a disheveled, dust-covered person, driven away from doors, if he were to swear by Allah, Allah would fulfill his oath." Impermissible: That which stems from arrogance and self-admiration, such as saying: "By Allah, Allah will not forgive so-and-so." This is to restrict Allah's mercy and nullifies good deeds.

One should avoid phrases that could carry a corrupt meaning, even if they might also carry a sound meaning.