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