It has been reported from Ummi Salamah Radhiyallahu 'Anha:
"Rasulullah Sallallahu 'Alayhi Wasallam preferred wearing, from among all clothing, the qamis (thowb)" (PT)
English reference (PT): Book 8, Hadith 55 (PT)
Arabic reference (PT): Book 8, Hadith 56 (PT)