Dought & clear, - Can he pray in the clothes he slept in?.

Do the clothes you wear to sleep become impure (so you are not allowed
to pray Salat in them.
Praise be to Allaah.
Firstly:
The basic principle with regard to clothes is that they are taahir
(pure), unless any najaasah (impurity) has gotten onto them, in which
case they must be purified.
Merely sleeping in clothes does not make them najis (impure); rather
they remain pure until it becomes certain that any impurity has gotten
onto them.
Shaykh Ibn 'Uthaymeen said: The basic principle with regard to a
person wearing clothes is that he (and they) are pure so long as he is
not certain that any impurity has gotten onto his body or clothes.
This basic principle is supported by the words of the Prophet
(blessings and peace of Allah be upon him) when a man complained to
him that he felt something during his prayer – referring to breaking
wind. He said: "Do not stop (praying) unless you hear a sound or
notice a smell." If the individual is not certain about that, then the
basic principle is that he remains pure. He may think it most likely
that his clothes have become contaminated with impurity, but so long
as he is not certain about it, the basic principle is that he remains
pure. End quote.
Majmoo' Fataawa Ibn 'Uthaymeen, 11/107
For more information please see the answer to question no. 12720
Secondly:
It is permissible to pray in clothes in which one has slept, so long
as they are pure and cover the 'awrah, although it is better and more
perfect to wear beautiful clothes that look good for prayer. That is
in obedience to the command of Allah, may He be exalted, in the verse
(interpretation of the meaning):"O Children of Adam! Take your
adornment (by wearing your clean clothes), while praying" [al-A'raaf
7:31].
Shaykh Ibn 'Uthaymeen (may Allah have mercy on him) was asked about
the ruling on praying in nightclothes and attending gatherings wearing
them. He said: There is nothing wrong with praying in nightclothes if
they are pure, whether one comes to the mosque wearing them or not,
unless those clothes will attract attention and criticism, and people
will talk about him in their gatherings because of that. People should
avoid anything that may be a cause of people backbiting about them.
End quote.
Majmoo' Fataawa Ibn 'Uthaymeen, 12/362
And Allah knows best.