"He was called from the side of the valley, on the right, in the blessed spot, from the tree, 'O Moses!'"
Muhammad said: "An" (that) is in the position of the accusative; the meaning is: He was called that, 'O Moses!' Similarly, "And that, throw your staff," is a conjunction referring back to it.
Surat al-Qasas (from verse 31 to verse 35).