Sungrass Egg

• WWizards of the Coast2008-08-01
  Official Ruling
  This is a mana ability, which means it can be activated as part of the process of casting a spell or activating another ability. If that happens you get the mana right away, but you don’t get to look at the drawn card until you have finished casting that spell or activating that ability.

Rulings via Scryfall