Ruling Question

[Clarkmeister]

Player A calls before the flop, so do 4 others. Flop comes, player A bets like 1/5th his stack. Player B is next with 3 others behind him. He says to Player A "will you call if I put you all in". Player A then says jokingly "I'll call whatever you want". Player B then goes all-in, the other players fold, and Player A folds but his cards haven't yet reached the muck.

Should Player A be forced to call Player B's bet?