משנה תורה, הלכות חמץ ומצה ז:ה-ח

(5) Anyone who has not said these three things on the night of the fifteenth has not fulfilled his obligation, and these are them: The Passover sacrifice; matsa; and marror. The Passover sacrifice for the sake of (to commemorate) that the Omnipresent passed over the homes of our ancestors in Egypt; as it is stated (Exodus 12:27), "And you shall say, 'It is the Passover sacrifice to the Lord, etc.'" Bitter herbs [to commemorate] that the Egyptians embittered the lives of our ancestors in Egypt. Matsa [to commemorate] that they were delivered. And these thing are called Haggadah (Recounting).

(6) In every generation, one must show himself as if he personally had come out from the subjugation of Egypt; as it is stated (Deuteronomy 6:23), "And He took us out from there, etc." And regarding this, the Holy One, blessed be He, commanded in the Torah (Deut. 5:15, 15:15, 24:22), "Remember that you were a slave" - meaning to say, as if you yourself had been a slave, came out to freedom, and were redeemed.

Hence when a person eats on that night, he must eat and drink while he is reclining in the way of freedom. And each and every one - whether man or woman - is obligated to drink four cups of wine on this night. We do not lessen them for him. And even for a poor person that is sustained from charity do we not lessen the four cups for him. The requisite amount of each of these cups is a reviit.

Even a poor person among Israel should not eat until he reclines. A woman does not need to recline; but if she is an important woman, she does need to recline. And a child with his father; and a butler in front of his master need to recline. But a student in front of his teacher may not recline unless his teacher gave him permission. And reclining of the right [side] is not reclining. And likewise one who reclines on his back or on his face - it is not reclining. And when do we need reclining? At the time of eating a kazayit of matsa and drinking these four cups. And if he reclines [during] the rest of his eating and drinking, he is surely praiseworthy. But if not, he does not need [to do so].