מדרש על שבת 2:4

And He formed the lumps of the dust of the first man into a mass in a clean place, (it was) on the navel of the earth. He shaped him and prepared him, but breath and soul were not in him. What did the Holy One, blessed be He, do? He breathed with the breath of the soul of His mouth, and a soul was cast into him, as it is said, "And he breathed into his nostrils the breath of life" (Gen. 2:7).