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