(a) Through the chain of Imam Ahmad a hadith like it is reported, but with this addition: We asked Hisham: What is "al-ikhtisar"? He said: That a man places his hand on his hips during prayer.
(b) Abu Hurayrah (may Allah be pleased with him) also explained it in the same way.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3565