It is narrated from Sayyiduna Thabit bin al-Dahhak (may Allah be pleased with him), and he was a Companion, that he said: "Whoever swears falsely by a religion other than Islam, he is as he said."
Hammad said: If you were to say that it is marfu' (that is, a saying of the Prophet (peace and blessings be upon him)), I would not mind.
Hadith Referenceالمعجم الكبير للطبراني / باب الثاء / 1312