Can I pray in pajamas or sweatpants?

The two conditions that matter

• Clean. Your clothes must be free of impurities such as urine or blood. Sweat is pure, so clothes you slept in are fine unless you can see or know of a real impurity. Parents of babies should check for urine on knees and shoulders.
• Covering. The required parts of the body must stay covered in every position, in fabric that does not show the skin.

The style of the clothing is a matter of etiquette. The same rules apply to every outfit. See Can I pray in jeans?

For men

Pajama trousers and sweatpants cover the awrah, which for a man is from the navel to the knee. Short pajama shorts and boxers are the problem, since they often leave the thighs uncovered. Put on trousers or a long pair of shorts before praying. Also check that the waistband holds, because a loose drawstring can slip when you go into sujood.

For women

A woman's prayer clothing must cover everything except the face and hands, including the hair, neck and arms. Hanafi scholars allow the feet to be uncovered, while the Shafi'i and Hanbali schools ask for them to be covered. Pajamas with short sleeves, three-quarter legs or a deep neckline need a cover-up. A long cardigan, a prayer dress and a large scarf do the job in seconds. See What do I have to cover when praying at home alone?

Is it disrespectful to pray in sleepwear?

A man once asked the Prophet ﷺ about praying in a single garment, and he replied, "Has every one of you got two garments?" (Sahih al-Bukhari 358). The point is that people pray with what they have, and no special outfit is required. At the same time, the Quran says to dress properly whenever you are at worship (Quran 7:31), and scholars recommend wearing better clothes when you can. That is a recommendation, not a condition.

So a clean pair of pajamas that covers you is valid. Praying Fajr in your sleepwear is far better than missing it or delaying it while you hunt for an outfit.