Iago sez it to Roderigo actually ... not to Cassio in Othello ...

“Put money in thy purse. Follow thou the wars; defeat thy favor with an usurped beard. I say, put money in thy purse.�?Iago says these words to Roderigo, urging Roderigo to turn his land and other material possessions into ready cash. Iago’s repetition of the saying “put money in thy purse,�?shows how he is very confident in what he is stating ... even !!