How to ask for same salary as my colleague?

So I joined in last May and my colleague also joined around 1 month back. We both are from tier 1 college (not same college) I am earning 12 LPA and he is earning 15 LPA. We work almost equally, in coming appraisal, I want to ask for same pay for same work ex. How can I talk about such topic without saying I know the salary of my colleague. And mind you I have slaved like hell, saturdays, sundays, holidays.

Open for all the suggestions.