It is narrated from Sayyiduna Sahl bin Sa'd (may Allah be pleased with him); he said: "I never saw the Messenger of Allah (peace and blessings be upon him) raise both his hands in supplication, whether on the pulpit or anywhere else, but I saw him (peace and blessings be upon him) do like this," and he pointed with his index finger and joined his middle finger with his thumb.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5999