What is the ruling on someone who sold Viagra pills to a married man who was healthy, and then the buyer died the next day, while the seller was ignorant of the cause of death?

There is no criminal liability on the drug seller for the death of the buyer, because he did not directly commit the killing or cause it. The seller is merely a seller, and selling beneficial medicines for needs is not causing death. The buyer bears responsibility for himself if he takes the medicine incorrectly. Allah Almighty said: (And every soul earns not [consequences] except upon itself, and no bearer of burdens will bear the burden of another). The physician is not liable if he performs his work according to correct medical principles, so it is even more appropriate that the pharmacist who merely sells the medicine to whoever requests it should not be liable. However, the seller is advised not to dispense dangerous medicines or those that require a physician's guidance except with an approved medical prescription, in accordance with His saying, the Almighty: (And cooperate in righteousness and piety, but do not cooperate in sin and aggression).