Answered by Shaykh Hamza Karamali, SunniPath Academy Teacher
Do we have to wear jilbabs? If not, does that mean we can pray with pants?
In the Name of Allah, Most Merciful and Compassionate
One of the conditions for the validity of the prayer is clothing ones nakedness. (see Reliance, section f5)
Shaykh Abd Allah Ba Fadl (Allah have mercy on him) said in his famous text, al-Muqaddima al-Hadramiyya (also knows as Masail al-Talim):
A condition of the clothing (satir) is that it prevent the colour of the skin (BK: from being perceived in a conversational setting (majlis al-takhatub) by someone of average eyesight, even if it reveals the form of the body (wa in hakaa al-hajm)) (Bushral-Karim, 1.92)
It would therefore be valid to pray in tight clothing.
Praying in tight clothing is, however, disliked (makruh) for women and better not to do (khilaf al-awla) for men. (Hashiyat Abd al-Hamid ala Tuhfat al-Muhtaj, 2.112)
The Reliance mentions that is recommended for women to pray in a jilbab (full length shift). It says:
f5.6 It is recommended for a woman to wear a covering over her head (khimar), a full length shift, and a heavy slip under it that doesnt cling to the body. (Reliance of the Traveller, 122)
The following section explains the recommended clothing for men during the prayer:
f5.7 It is recommended for a man to pray in his best clothes, and to wear an ankle-length shirt and a turban. (Reliance of the Traveller, 122)
Outside the prayer, women should not wear tight clothing. If women can modestly cover themselves with something other than a jilbab (such as a loose skirt and a long shirt, or something else), that would also be okay.
And Allah knows best.