May Allāh forgive me, I was standing in salah and got distracted with sexual thoughts and I started imagining having intercourse and then I accidentally did a small thrusting motion as if I was having intercourse. Am I a kafir for this?

Ustadh AbdulAziz al-Haqqan

No you uave a waswas i believe correct me if i am wrong. But what u did is very wrong, where is the khushu akhi? Why would u think about this in salah! Shun these ideas away baraka Allahu feek.