676. If a person fears that using water may endanger his life, or fears that he may develop a sickness or a defect, or that his sickness may be prolonged, become severe, or become difficult to cure, he should perform tayammum instead. However, if hot water does not cause harm to him, he should perform his wuÃÙ or ghusl with hot water.
677. It is not necessary that he be certain that water is harmful for him; rather, if he even fears that it may be harmful for him, and his fear is considered to be reasonable by the people, he should perform tayammum instead.
678. If a person is afflicted with an eye disease, and water is harmful for his eyes, he should perform tayammum instead.
679. If a person performs tayammum being certain of the harm (of using water), or fearing its harm, but realizes prior to offering prayer that it is not harmful for him, his tayammum will be void. If he realizes this after offering his prayer, and the allocated time for the prayer has not yet elapsed, he should offer his prayer with wuÃÙ or ghusl. However, if the allocated time has elapsed, then its qaÃÁ is not obligatory.
680. If a person performs wuÃÙ or ghusl, being certain or satisfied that water is not harmful for him, and he later realizes that it was harmful for him, his wuÃÙ or ghusl will be void if the harm is to an extent that inflicting such harm on oneself is forbidden.