Possession is nine tenths of the law
Definition 1 of 1
Pro Tip 1/3Metaphorical Use
This phrase is often used metaphorically to suggest someone's strong claim due to their control or use of something. 
He's been using the workshop for years, so possession is nine tenths of the law when debating his claim.
Pro Tip 2/3Context Matters
The phrase is typically used in informal settings and may not be taken literally in actual legal disputes. 
Sure, the bike was mine originally, but he rides it daily—possession is nine tenths of the law, I guess.
Pro Tip 3/3Not Always True
Understand that this phrase is a principle, not formal law, and may not hold up in court or in serious disputes. 
I found the lost phone, but possession is nine tenths of the law won't work if the owner shows up with a receipt.