Imam Sajjad (peace be upon him): Allah has an angel called "Kharqa'il" who has eighteen thousand wings, and between each two wings is a distance of five hundred years' travel. It occurred to him: is there anything above the Throne? So Allah doubled his wings, and he came to have thirty-six thousand wings, with a distance of five hundred years between each two wings. Allah revealed to him: fly, O angel. He flew for twenty thousand years and did not reach the top of a single pillar of the Throne. Allah then doubled his wings and his strength, and he flew for another thirty thousand years and still did not reach it. So Allah revealed to him: O angel, even if you were to fly with your wings until the blowing of the trumpet, you would not reach the leg of My Throne. The angel said: سَبِّحِ اسْمَ رَبِّکَ الْأَعْلَی [Glorify the name of your Lord, the Most High]. And Allah sent down سَبِّحِ اسْمَ رَبِّکَ الْأَعْلَی, and the Prophet (peace be upon him and his family) said: "Make it the dhikr of your prostration."