The Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, said: "A shirt (qamis) is sufficient for a man in prayer if it is thick (non-transparent), and a woman must wear a gown (dir‘) and a head covering (khimar) in prayer." The explanation of this has already been fully discussed previously, so there is no need to repeat it, Allah سبحانه وتعالى willing.