Cash in hand, proof of funds?

[Account Closed]

Hello BP community! I've been hanging out in the shadows for some time now reading posts, listening to podcasts etc. Well after a year plus of research its time to make an offer on my first deal. I need to get some form of "proof of funds" letter together. So here's my question. I Have all the cash for the deal. Only about a third of it is in the bank and the rest is cash in hand. Obviously I can deposit it in my bank account, then just get a letter from the bank saying I have x amount in my account. My concern is if i deposit a large sum of money in my account will I have to pay taxes on it or have any other red flags raised? Ive been saving for almost 5 years and everything has come from my employment so its already been taxed. I'd hate to be taxed again or raise my current tax bracket etc. Am I over thinking this? Any ideas or input would be greatly appreciated! 

Thanks