How to explain the source of funds transfered to my bank account for a UK visa? [duplicate]

You are absolutely going to have to provide evidence to support the source of these funds.

Frankly you are already describing lying on your immigration form, something that is going to get you a refusal and possibly a ban on further applications. You might claim "My Mom gave me this money for no specific purpose and I decided to use it on this trip" but that's going to be hard to believe.

The transfer into your account already looks suspicious, and without lots of explanation is going to get you a refusal. The trick of putting extra borrowed money temporarily into an account to make it look better is extremely well known, and even if this is not your intention, having financials that look like this will be reason for rejection. Your application will not be the first that the visa officer has seen that looks like this - probably not the first that day.

A 'bank transfer form' and 'debit advice' are not enough. They only prove that you received the money, which your statement already shows. You absolutely need to show that the money originated from your Mom, which means showing her bank statements. Probably helpful would be an affidavit that this money is yours to keep, and not a loan.

Moreover if your Mom has only the money she gave you in her account, then even the statements are not going to help. You would need to include other financial records to show that she can afford to give you this money, and where she got the money from. No sensible person gives away all the money they have in the world just so that their son can take a vacation in the UK, and the visa officer will not believe she is doing it.