Praise be to Allah.
In the answer to question no. 105330 we stated that it is prescribed to send blessings on the angels.
But in the tashahhud doing that is not prescribed, because what must be done is to recite only that which was proven from the Prophet (peace and blessings of Allah be upon him), without adding anything to it.
Shaykh Salih al-Fawzan was asked: Should blessings be sent on the angels in the tashahhud as they are sent on the Prophet (peace and blessings of Allah be upon him)?
No, the blessings that are mentioned in the tashahhud should be limited only to that which is narrated, but when we say al-salamu ‘alayna wa ‘ala ‘ibaad-Allah al-saliheen (may peace be upon us and upon all the righteous slaves of Allah), this includes every righteous slave in heaven and on earth, which includes the angels.
Majmoo’ Fatawa al-Shaykh Salih al-Fawzaan.
And Allah knows best.