The ruling on saying "Peace be upon you, O Prophet" after his (peace and blessings be upon him) death

Question:
The statement of Ibn Mas'ud (may Allah be pleased with him) : He said, "When we were in the time of the Prophet (peace and blessings be upon him), we used to say: 'Peace be upon you, O Prophet.' And when he passed away, we used to say: 'Peace be upon the Prophet'?"

Answer:
No, this is the independent reasoning (ijtihad) of Ibn Mas'ud. The Prophet (peace and blessings be upon him) taught them and did not say this to them. The Prophet (peace and blessings be upon him) taught them to say: "Peace be upon you, O Prophet," and he knew that he would die (peace and blessings be upon him). They used to say it while he was absent; those in Iraq, those in Sham, and those in Yemen used to say this while he was absent from them, and they were in Makkah and other places. So it is better to say what the Prophet (peace and blessings be upon him) taught: "Peace be upon you, O Prophet," like this. And if one says: "Peace be upon the Prophet," as Ibn Mas'ud (may Allah be pleased with him) said, there is no harm. But the Sunnah is that the phrases the Prophet (peace and blessings be upon him) taught his Companions are more preferable, more preferable than the independent reasoning of Ibn Mas'ud (may Allah be pleased with him).