“I once asked abu al-Hassan (a.s.), about the case of a man who places himself for hire, and he said, 'It is permissible and there is no harm in it as long as he is sincere to the best of his ability. Musa (as) placed himself for hire and stipulated, saying, "If you wish, [I will work] for eight years, and if you wish, for ten." And Allah, the Exalted, revealed concerning this: 'That you serve me for eight years; but if you complete ten, that will be [a favor] from you.' (28:27)“