פירוש על קידושין 65:6

The baraita states teaches that one does not need to rise before a sage in a bath-house or bathroom (toilet). Nevertheless, R. Shimon son of Rabbi [Yehudah Hanasi] is offended when R. Hiyya does not stand in front of him even though he is in a bath-house. He even goes and complains about it to his father.