Luis de Molina  

"“man is dominus not only of external good, but also of his honor and fame; he is also dominus of his own liberty, and in the context of the natural law can alienate it and enslave himself. It follows that a man who is not subject to the law sells himself unconditionally in someplace where the relevant laws allow him, then that sale is valid” (Luis de Molina cited in Natural Rights Theories: 54, Tuck 1981)."

Latin original from Molina's De iustitia et iure, Disp. 33, coi. 162:

‘'Tertius titulus est emptio etvepditio. Ponendum in primis est, hominem, sicut non solum externorum suroumbonorum, sed etiam proprii honoris & famae est dominus [...] sic etiam dominumesse suae libertatis, atque adeo stando, in solo iure naturali; posse eam alienare,seque in servitudinem redigereSi tamen quis suae libertatis prodigus esset,absque rationabili causa se servituti subiiciens, non minus imo magis peccaret,quam si non solum pecuniarum sed etiam honoris et famae [...] esset prodigus”