In the Name of Allah, The Most Merciful, The Bestower of Mercy
Imaam ash-Shaafi’ee [d. 204], may Allah have mercy on him, said (1):
A man can pray in pants, if they conceal what is between the navel and the knees. However, prayer in an izaar is more concealing and more beloved.
It is more beloved, to me, that he does not pray except that there is something on his shoulder, [the tail of] a turban, or other than it, even if it is a rope that he places on it.
(1) See “al-Umm”, 2/202 – Dar al-Wafaa.