Bhagavatapurana 3.31.2

3.31.2

kalalaṃ tv eka-rātreṇa pañca-rātreṇa budbudam /
daśāhena tu karkandhūḥ peśy aṇḍaṃ vā tataḥ param //

2. In the course of a night the mingling of the seed and blood takes place; in five nights it becomes a round semi-solid mass; in ten days it becomes as hard as an apple, or it may become a ball of flesh or an egg;