What is the Crosby, Stills, and Nash song that has a long guitar part in the beginning with no lyrics?

i heard a song on the radio on my way to church the other day and my dad had said it was from crosby stills and nash. the song was just guitar in the beginning for a pretty long while. it sounded like maybe more than one guitar. i can't remember if there were lyrics in it though. if there were, they came later in the song. it was a beautiful song that i'm trying really hard to look for, please help?