Hello. I have a problem.
Today I meant to pray something, and my tongue said something else that I didn’t mean and don’t want. I don’t want it to happen since I didn’t mean it - my tongue said the opposite of what I intended. I know god is merciful and knows how what’s in my heart but I am afraid. Is there anything I can do so that god could forgive me for my stupidity and lack of concentration?

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 is His slave and Messenger.

Do not worry and do not grieve; nothing will result because of this error. Allah Says (what means): {And there is no blame upon you for that in which you have erred but [only for] what your hearts intended.} [Quran 33:5]

Therefore, do not think about this mistake and strive to supplicate Allah asking any goodness you wish.

Allah Knows best.