What is the ruling on folding the edge of the prayer rug during prayer to keep track of the number of rak'ahs?

The basic principle is that the action performed by the father is not permissible, because it is not one of the actions of prayer. However, if he is afflicted by obsessive-compulsive disorder (waswasah) or is very forgetful, he might have an excuse for his action. The jurists have mentioned the permissibility of similar actions, such as moving a ring to count the rak'ahs for fear of forgetfulness, or counting the takbīrāt of the funeral prayer with the fingers. Muhammad and Abu Yusuf from the Hanafis are of the opinion that counting verses and tasbeeh with the hand during prayer is not disliked (makrooh), whereas Abu Hanifa considered it disliked. In summary, one should refrain from that action if it is possible to keep track of the number of rak'ahs. If it is not possible, then we hope there is no harm upon him, because this action is minor and prayer is not invalidated by it.