Is the purification (Tahara) using sun-heated water disliked (Makruh)?
Chapter on what purification is achieved with regarding water
Al-Mughni
Book of Purification
Primary text
The primary ruling is that purification using sun-heated water is not disliked (Makruh). This position is taken because the water was heated by a pure substance, analogous to water found in natural pools or rivers, or water heated by fire, or water whose heating by the sun was not intentionally sought. The premise that harm differs based on intentionality is unfounded. Furthermore, the evidence cited against its permissibility is deemed unestablished (Ghair Thabit). This evidence is narrated by Khalid bin Ismail, who is considered abandoned in Hadith transmission (Matruk al-Hadith), and Amr bin Muhammad al-Aasam, who is considered to narrate rejected Hadith (Munkar al-Hadith), according to Al-Daraqutni. Al-Daraqutni also stated that the narration is not soundly transmitted from Al-Zuhri.
Supporting text
The position of Imam Al-Shafi'i is that purification using water intentionally heated by the sun in vessels is disliked (Makruh). This dislike is based solely on medical reasons, citing a narration attributed to Aisha, may Allah be pleased with her, stating that the Messenger of Allah, peace and blessings be upon him, forbade her from using water heated in the sun, saying it causes leprosy (Baras). Abu Al-Hasan Al-Tamimi favored this view. Additionally, practitioners of medicine interviewed stated they do not recognize any causal effect of such water in causing harm.