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