Is the prayer valid in forbidden clothing?
Machine translationRead the Arabic original
The Shaykh : If the clothing is forbidden, then it does not cover the 'awrah (part of the body that must be covered) validly, and in that case, praying in it is like praying naked. This is the well-known position in the school of Imam Ahmad (may Allah have mercy on him).
Source
قناة «فضيلة الشيخ محمد بن صالح العثيمين»، 40- هل تصح الصلاة في الثوب المحرَّم؟ II فوائد من الدروس الفقهية من المحاضرات الجامعية لابن عثيمين — youtube.com
The Arabic text is a machine transcription of the audio recording.