What is the ruling on fearing death, and is one who fears it sinful, especially if that leads to avoiding the causes of death, such as jihad?

Fear of death is innate and not blameworthy in itself, but it becomes blameworthy if it leads to abandoning acts of obedience or duties. The cure for this is to remember that fleeing from death does not delay one's appointed time, and approaching it does not diminish it.

A wise person does not disobey Allah's command out of fear of something from which there is no escape, for fleeing does not prolong life, and approaching it does not shorten it. If a servant dies in obedience to Allah, he is destined for a great good, for the eternal life of the Hereafter is the perpetual bliss for the pious.

Recalling Allah's reward in the Hereafter makes it easier for a Muslim to face dangers, obey commands, and avoid prohibitions. Emulating the lives of the righteous and seeking Allah's pleasure encourages the adoption of these noble virtues. A Muslim must entrust his affairs to Allah and rely upon Him, asking Him to grant him a good death, to make life an increase in all good, and death a relief from all evil.