Brother transferred our joint property in Delhi without my consent?

I just found out that my brother sold our joint family property in Delhi last month without informing me. This property was left to us by our late father. I didn't sign any documents or give my consent for this transaction. He says everything was legal, but I feel betrayed and don't know what to do. I'm worried he's going to take the money and disappear. How can I contest this sale and protect my rights?