Not making a vow verbally

Q: I remember that I did not make any vow or verbally utter any vow to read 8 rakaat shukriya nafil namaz. Only a thought came and I read. Still, that thought is confusing me that it was a vow and I am getting scared of those thoughts. I am getting thoughts that I made vow verbally, but I don't remember making a vow verbally. I am confused whether it was verbally or not.