His statement: "O you who have believed, do not raise your voices" [Quran 49:2], the interpretation of al-Hasan: that some people among the hypocrites used to come to the Prophet and raise their voices above his voice, intending by that to annoy him and belittle him. So He attributed them to what they were granted of faith in appearance, saying: "O you who have believed, do not raise your voices above the voice of the Prophet or be loud to him in speech like the loudness of some of you to others" [Quran 49:2]. He says: Do not say: "O Muhammad," but rather say: "O Messenger of Allah," and "O Prophet of Allah," "lest your deeds become worthless [without your perceiving it]."

Muhammad says: The meaning is: so that would be a cause for your deeds to become worthless.