It's a slow song.. and it sound like a male group... its called "one love".. In the break down part of the song they say "one step, one love.. (something like that)

Bob Marley's song One Love (BOB MARLEY - ONE LOVE Lyrics (http://www.seeklyrics.com/lyrics/Bob-Marley/One-Love.html)) is the only one that I have personally heard. but there are other songs with the same title by Trey Songz (Trey Songz - One Love Lyrics (http://www.lyricsmode.com/lyrics/t/trey_songz/one_love.html)) and Blue (BLUE - ONE LOVE Lyrics (http://www.seeklyrics.com/lyrics/Blue/One-Love.html)). The one by Nas seems to be an extremely long shot.

U2 also did a song called One Love... Brilliant :)

http://youtu.be/HjdyOY3rCjs