It was narrated from Ibn ‘Abbas (رضي الله عنه) that

Two men referred a dispute to the Prophet (ﷺ), and the Prophet (ﷺ) asked the claimant for proof. He did not have any proof, so he asked the defendant to swear an oath and he swore by Allah, besides Whom there is no other god. The Messenger of Allah (ﷺ) said: "You did it, but you will be forgiven for your sincerity in saying there is no god but Allah."