Exodus 2:3

And when she could not longer hide him, she took for him an ark of bulrushes, and daubed it with slime and with pitch, and put the child therein; and she laid it in the flags by the river's brink. When it became increasingly difficult to hide the boy from the eyes and ears of prying Egyptians, the mother constructed for him a small chest, or ark, out of the papyrus reeds that grew on the banks of the Nile, making it water-tight by means of asphalt and pitch, and placed this in the rushes on the brink of the river.