The First Revelation to Musa

Allah, the Exalted, says,

فَلَمَّآ أَتَاهَا

فَلَمَّا أَتَاهَا (So when he came to it - 20:11): means that he approached the fire which he had seen from a distance. Musnad by Ahmad, on the authority of Wahb Ibn Munabbih (رح) reports that when Sayyidna Musa (علیہ السلام) drew near the fire he saw a very strange scene. A fire was blazing on a green tree without scorching even a leaf or a branch. On the other hand the flame added manifold to the beauty and the freshness of the tree. He stood there quite a while watching this strange sight waiting for a chance to pick up a piece of burning wood. At last he collected some dry grass and tried to light it but as soon as he pushed the grass towards the fire, it retracted. It is also related that the fire advanced towards him and he drew back in consternation. Consequently he was unable to collect any fire. And as he stood, not knowing what to do, a mysterious voice called him. This happened in a plain called Tuwa which was to his right side and at the foot of this mountain.