There's something cool about musicians quoting themselves. While there are many more than three examples, these are just some of my favorites. How about you? Let's get a long list going so someone can write a book about the subject. Give us the lyric and the two songs. (Try not to include concept album lyrics, like The Wall, or something, where songs come back throughout the album in different permutations.)
1a. "Every Little Thing She Does Is Magic" by the Police
1b. "O My God" by the Police
Following up in 1983 with one of their best-selling albums, Synchronicity, Sting used the same exact lyric toward the end of the song "O My God." (He'd go on to use it AGAIN on his solo album Ten Summoner's Tales in the track "Seven Days.")
2a. "Sexx Laws" by Beck
Put out in late 1999, as Y2K fears ridiculously gripped the world, Midnight Vultures contains two songs with the same lyric. Here it is first, in its most famous incarnation, off the first song on the album: I'm a full-grown man/But I'm not afraid to cry
2b. "Debra" by Beck
A totally different type of tune altogether, "Debra" is the final song on the album and contains every word in the above referenced lyric, hold the last ("cry").
3a. "She Loves You" by The Beatles
Released as a single in 1963, "She Loves You" is one of The Beatles all-time most popular tracks. In the U.K., it's still the best-selling Beatles single ever.
3b. "All You Need is Love" by The Beatles
Magical Mystery Tour came out four years later, and featured the hit "All You Need is Love." If you listen closely, you can hear the orchestra playing "Greensleeves" in the background (and elsewhere in the track, a lick from Glenn Miller's "In the Mood" and a little bit from Bach, as well.)