Sayyiduna al-Sharid bin Suwayd (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) passed by me while I was sitting like this: I had placed my left hand behind my back and was leaning on my hand. He (peace and blessings be upon him) said: "Are you sitting in the manner of those who have incurred [Allah's] wrath?"
(b) In the narration of Abd al-Wahhab: I was sitting in the mosque, having placed my left hand behind my back and leaning on my hand.
Al-Qasim said: The alyah of the palm means the thumb and the raised flesh beneath it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5920