daf bit: Yevamot 61

A mishna on today's daf teaches: a man may not abstain from the obligation of procreation ("be fruitful and multiply") unless he already has children. How many? Beit Shammai says two males (because Moshe had two sons, the g'mara says), while Beit Hillel says one male and one female, because "male and female He created them". The g'mara goes on to say that even if he is exempt from procreation, he is not exempt from living with a wife even if he has many children, because "it is not good for man to be alone". (61b)

By the way, the obligation to produce children is specifically on the man. Obviously two people need to be involved, but women are not commanded in this.