How to treat cash received on sale of fixed asset in the cash flow statement?

This depends very much on your future intentions.
Please remember:-

This is a one time item.
It is NOT repetitive.
The best way is to ear mark it for the
Replacement of the asset.

A mistake is made when because of it
You get anxious in paying other bills.
Once the money is spent , special procvision
Will have to be made to replace the asset.

Cash received from sale of fixed assets should be reported as cash inflows from investing activities "proceeds from sale of fixed assets"