Leviticus 12:4

And she shall then, counting from the eighth day, continue in the blood of her purifying three and thirty days, this making a total of forty days, during which she was to stay at home, although the restrictions of the first seven days were now made much lighter; she shall touch no hallowed thing, nor come into the Sanctuary, until the days of her purifying be fulfilled. Although free to perform the ordinary duties of the household, she could not take part in sacrificial meals, the Passover and other festivals, nor was she permitted to enter the court of the Sanctuary. The forty days were the symbolical time of purification, of exclusion from the world.