Offering Prayers with Trousers Folded above the Ankles

In terms of the validity of the prayer, there is no question that performing Salat with trousers folded up does not invalidate one’s prayer.

As for this being disliked (makruh) in Salat, it was explained in a previously posted answer titled: ‘Wearing Short-Sleeved Shirts’ that the Hanafi jurists (fuqaha) generally consider performing Salat in ways that are contrary to proper etiquettes (adab), such as rolling-up one’s sleeves to the elbows, to be Makruh. (Radd al-Muhtar, 1/ 640)

In light of this, it will be Makruh to perform Salat with one’s trousers folded-up if they are folded in an untidy and improper way, such that one would feel embarrassed to be in that state in noble gatherings; for example folding the trousers up to or close to the knees. However, if they are folded neatly and slightly, then it will not be Makruh.

As for the Hadith recorded by Imam al-Bukhari in his Sahih from Sayyiduna Abdullah ibn Abbas (Allah be pleased with him) that the Messenger of Allah (Allah bless him & give him peace) said, ‘We have been ordered to prostrate on seven bones, and to neither gather a garment nor hair’ (Sahih al-Bukhari 777), it refers to lifting or gathering and tying one’s garment from the front or back before going into prostration (sujud) to prevent it from touching the floor. This is prohibitively disliked, as it goes against the spirit of Salat which is based on ultimate humility. (See: Imdad al-Fattah sharh Nur al-Idah P: 357 and Tahtawi ala Maraqi al-Falah P 350)

And Allah knows best