Write an application to the principal of your school,requesting him/her to grant you leave of absence of three days.
Nov 25, 20xx
Subject: Request to grant a leave of five days
With due respect, I want to state that I need three days' leave to attend my sister's wedding.
My elder sisters wedding is to be solemnized at Chandigarh on Dec 14, 20xx. My entire family will be leaving for the wedding on December 13. We would be returning to Delhi only on the 15th of the month.
I, therefore, request you to grant me leave for three days from December 13-15. I shall be extremely grateful to you for the same.