Assalamualaikum, I was wondering if my prayer is valid if I accidentally said raasullah instead of abdoho wa raasulh in the tashahudd

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu`alayhi wa sallam, is His slave and messenger.

Your prayer is not invalidated by your saying “And I bear witness that Muhammad is the Messenger of Allah” instead of “And I bear witness that Muhammad is His servant and His Messenger.” It is reported in the Saheeh of Imam Muslim on the authority of Ibn 'Abbaas that he said: “The Messenger of Allah, sallallaahu`alayhi wa sallam, used to teach us Tashahhud as he would teach us a Surah of the Qur'an. He used to say, “All services rendered by words, acts of worship, and all good things are due to Allah. Peace be upon you, O Prophet, and Allah's mercy and blessings. Peace be upon us and upon Allah's upright servants. I testify that there is no god but Allah, and I testify that Muhammad is the Messenger of Allah.”

So, this sentence is mentioned in an authentic Hadeeth.

Allah knows best.