In the Sikh dharma, contrary to the popular notion, the Number 13, if it comes randomly in your life, is considered very lucky.

The story behind is.
When Shri Guru Nanak ji was doing his teenager internship as an accountant, He was cross checking an expense inventory . 

When he got to the 13th item on list, He got a divine flash, (in punjabi–the verbal Tera (yours) is similar to terah (thirteen) ) 

In a trance, He started adding 13 to the rest of the items chanting (all is yours — sab tera hai — EVERYTHING IS YOURS) he did this for almost all the inventory, till his Boss entered and saw him half dazed and adding 13 units to every item.
The Boss was enraged and snatched away the inventory from  Guruji‘s  hands, kicked him out of  the office and gave the inventory to his senior accountant to rectify the “mistakes” 

After a while, the senior accountant came back with his face in his hands to the boss.
He said “It seems to be a miracle, that despite the young lad who added 13 everywhere, the final figure/sum is perfect.


Sab Tera
Courtesy Shonan Talpade