The ruling on sending blessings upon the Prophet in the tashahhud with other than what was transmitted

Question:
A man asks about the ruling on his prayer. He says: "When I was sending blessings upon the Prophet (peace and blessings be upon him) during the prayer, I said: 'O Allah, send blessings upon Muhammad,' and then I concluded the prayer. That is to say, he did not send the complete blessings upon the Prophet."

Answer:
The prayer is valid, but he left off what is prescribed; because when the Prophet (peace and blessings be upon him) was asked, he said: , and there is no evidence indicating that it is obligatory. However, as a precaution, it should be recited in the final tashahhud, and this is emphasized to avoid scholarly disagreement.
Q: So the obligatory part is to say only: "O Allah, send blessings upon Muhammad"?
A: He should recite it in its proper form and manner: "O Allah, send blessings upon Muhammad, and upon the family of Muhammad, as You sent blessings upon the family of Ibrahim, and bless Muhammad, and the family of Muhammad, as You blessed the family of Ibrahim." And if he combines the two families, it is better: Muhammad and his family, and Ibrahim and his family.
Q: Is it obligatory or a pillar?
A: A group of scholars hold that it is a pillar, another group holds that it is obligatory, and a third group holds that it is a recommended practice. However, in any case, it should not be left off, to avoid scholarly disagreement, in the final tashahhud.