What is the ruling on a judge administering an oath to an atheist who does not believe in the existence of the Creator, and what is the legitimate wording of an oath for him, if one exists, and how should he be dealt with if there is no evidence for the plaintiff and the oath is not legitimate?

An oath can only be taken by Allah the Almighty, whether before a judge or otherwise. This applies to Muslims, disbelievers, and atheists alike, based on the Almighty’s saying: {Then they both swear by Allah}, and the Prophet's (peace be upon him) saying: “Whoever takes an oath, let him swear by Allah or remain silent.” Judge Shihabuddin Ibn Abi al-Dam al-Shafi'i explained the benefit of making an atheist, who does not believe in the existence of Allah the Almighty, swear an oath in two matters: First, to enforce the judgment upon them according to what Allah has revealed, and second, to increase their sin and hasten their retribution.