Is it permissible for a man who is obliged to provide for his family, and whose health is weak, to take on a strenuous full-day job that may harm his health, when he cannot find an alternative?

A person who cannot find means to provide for his family must earn a livelihood in a permissible manner, unless he would incur certain harm from doing so, based on the Prophet's (peace be upon him) saying: "There should be no harm nor reciprocal harm." However, a mere possibility of harm does not negate the obligation.