Pattern of Rebirth

Enchant creature
When enchanted creature dies, that creature's controller may search their library for a creature card, put that card onto the battlefield, then shuffle.

Ultimate Masters

Enchant creature
When enchanted creature dies, that creature's controller may search their library for a creature card, put that card onto the battlefield, then shuffle their library.

World Championship Decks 2000

Urza's Destiny

When enchanted creature is put into a graveyard from play, that creature's controller may search his or her library for a creature card and put that card into play. If that player does, he or she then shuffles his or her library.

Because the “search” requires you to find a card with certain characteristics, you don’t have to find the card if you don’t want to.

Searching for a creature card is optional.