Read the Runes

Instant

Draw X cards. For each card drawn this way, discard a card unless you sacrifice a permanent.

2004-10-04:
You are never forced to sacrifice any permanents. You can choose to discard your entire hand if your hand is smaller than the number of cards you are required to discard.
2004-10-04:
You draw the cards, then sacrifice any permanents you want to sacrifice, then discard the required number of card from your hand. There is no chance to play any cards in between these actions.