Sodium cyanobohydride es a reductant, it transfer hydride to imine.

For example in this paper

http://pubs.acs.org/doi/abs/10.1021/bc400018u

Aldehyde reacts with the terminal amine to form and imine that is reduce to an amine,

you end having a C-N bond That is a reductive amination reaction.

Dear Pooja Nanda ,

Sodium cyanobohydride is just reduce the amine to imine., its just reductive amination  main agent out of that no role for this., without this only 20-30% of reaction yield we will receive.,

Good Luck & Regards

R.Selva....

yah i agree R.Selva.. and Guillermo R. Labadie answer

Dear Selva,

Thanks for the information.