1. sudo vi /etc/apt/sources.list
2. Un comment the line
   deb-src http://archive.raspbian.org/raspbian/ jessie main contrib non-free rpi

deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib non-free rpi
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
deb-src http://archive.raspbian.org/raspbian/ jessie main contrib non-free rpi