Tax Question - FSBO Investment Property

[Michael Simmons]

Situation: Selling an investment property FSBO (we've never occupied the residence). I will keep the mortgage in my name and make mortgage payments. New "owners" will pay me monthly. They have 5 years to secure funds. When do I claim the sell of the investment property? 1) When we sign the FSBO contract or 2) When they secure funds to pay me off? If it's 1) How do I handle payments in the interim?

Thank you in advance.