Jamieson, Fausset and Brown on 2 Chronicles 7:3

3. all the children of Israel ... bowed themselves with their faces to the ground upon the pavement--This form of prostration (that of lying on one's knees with the forehead touching the earth), is the manner in which the Hebrews, and Orientals in general, express the most profound sentiments of reverence and humility. The courts of the temple were densely crowded on the occasion, and the immense multitude threw themselves on the ground. What led the Israelites suddenly to assume that prostrate attitude on the occasion referred to, was the spectacle of the symbolical cloud slowly and majestically descending upon the temple, and then entering it.

2Ch 7:4-11. Solomon's Sacrifices.