It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Placing the hands on the hips in prayer is a source of comfort for the people of Hell."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3566