How do we greet the Prophet (peace and blessings be upon him) in the tashahhud?

Question:
It is narrated from Ibn Mas'ud (may Allah be pleased with him) that he said: We used to say in the tashahhud during the lifetime of the Prophet (peace and blessings be upon him): "Peace be upon you, O Prophet, and the mercy of Allah and His blessings." And after his passing, we used to say: "Peace be upon the Prophet, and the mercy of Allah and His blessings." Is this correct? And do we say it in the tashahhud?

Answer:
The prescribed practice is for them to say what the Prophet (peace and blessings be upon him) taught the Companions. He taught them to say: So we say as the Messenger (peace and blessings be upon him) taught us. He taught the Companions and did not tell them to change it when he died. He taught them while they were traveling, going to distant lands, saying: "Peace be upon you, O Prophet, and the mercy of Allah and His blessings." This means they are making du'a' for him. "Peace be upon you" is a du'a' for him, for safety, mercy, and blessing. "O Prophet" means bringing him to mind; "O Prophet" does not mean calling him directly; they are making du'a' for him. "Peace be upon you" means for you is safety, for you is well-being, mercy, and blessing from your Lord. It is a du'a' for him (peace and blessings be upon him); he is not being called, but you are asking Allah for his safety, mercy, and blessing.
And whoever says: "Peace be upon the Prophet, and the mercy of Allah and His blessings," there is nothing wrong with it, but it is better to say: as the Prophet (peace and blessings be upon him) taught the Companions: This is what the Prophet (peace and blessings be upon him) taught his ummah, and he died upon that, (peace and blessings be upon him).