Abu Sa'eed Khudari Radiyallahu 'Anhu says:
"When Rasuluilah Sallallahu 'Alayhi Wasallam sat in the rnasjid, he sat in the qarfasaa posture' (ID)
English reference (ID): Book 20, Hadith 122 (ID)
Arabic reference (ID): Book 21, Hadith 129 (ID)