Hadhrat Thanvi said that closing the eyes in Salaah is against the Sunnah but permissible without karaahah.

Answer

We differ with Hadhrat Thanvi on this issue. If it is Sunnah to perform Salaat with open eyes, then it will most certainly be Makrooh Tahrimi to perform Salaat with closed eyes without valid reason. Adopting closed eyes as a permanent practice is not permissible because it is in violation of the Sunnah. It is not permissible to abandon a Sunnah without valid reason.

An Aalim mureed of Haaji Imdaadullah (Rahmatullah alayh), narrated that once he had performed two raka'ts Nafl with deep concentration and considerable care. During the night, in a dream, his Salaat was shown to him as a damsel of Jannat of stunning beauty. When he looked carefully at her, he observed that she was blind. Haaji Imdaadullah spontaneously informed him that she was blind because he had performed the Salaat with closed eyes.

THE SUNNAH