It is a house rule.The actual prined rules allow you to collect rents when in Jail.
One of the things about Monopoly ios the number of house rules that have sprung up. ANother biggie if that the fines and taxes are put under the free Parkng space, and whoever lands on that space gets the money.
And most of these house rules have a negative impact in that they prolong the game. A game of Monopoly, when played strictly by the printed rules, last arond 90 Minuts to a hour. It is when the house rules are used you have the extremly long games thea turn it into "Monotony".
Almost all of the house rules keep money in cirulation, which prolonges the game.Players can stay in the game longer without going bankrupt and the game ends when all but one Player goes bankrupt.