Is one who takes dispensations in most of his acts of worship and religion because of waswasah (obsessive-compulsive disorder) sinful, such as combining prayers, or performing tayammum instead of washing the feet, and completing the prayer despite intending to interrupt it?

Many scholars permit taking some concessions (rukhs) when there is a need, and the person afflicted with waswas (obsessive whispering) is among those most in need of such concessions. Therefore, there is no harm for you in adopting what makes worship easier for you, provided that you verify the authenticity of the scholar's statement. As for performing tayammum (dry ablution) for your leg, it is not permissible as long as you are able to wash it in any way that does not lead to an imbalance. We hope that combining the prayers is permissible for you if the waswas becomes severe, because it is a type of illness, and some scholars have permitted it for illness or for absolute need.