Swizz Beatz and Nas got together for a collaboration record called "Summer On Smash" for Nas' newly released Life Is Good album.  Swizz and Nas actually worked on a few other songs in the studio as well however only "Summer On Smash" made its way on Nas' album.  During a brief interview with MTV News, Swizz spoke about the actual experience of working with Nas in the studio for the album and how as a producer, he is a big fan of Nas and really wanted to work with him for Life Is Good.

"We collaborated on a couple of other joints also, it was a fun time working with my Virgo brother.  I listened to the album and the whole entire album was super lyrical, it had all the different elements, I just think that it was perfect because it was dropping in the summer.  You know as a producer you're a fan of the artist so you have stuff like, 'Yo I need him to do this.'"

Source: hiphopblog.com