Yes, you do. There's a question on the Appendix 2 application form that asks for the source of the savings (question 3.75)... you write it in there.
What is your savings source?
If the money has just come from building up savings over the years, then you don't need to provide anything else.
But, if the money has come from a different source in a lump sum, then you should provide evidence of that.
For example:
- if it was a gift, you provide a letter from the person who came from, stating that is is a gift and will not be repaid
- if it comes from an inheritance, then you can provide evidence of the inheritance
- if it comes from the sale of property, then you can provide evidence of the sale
etc.