And concerning the preservation of health, He said:
“But whoever among you is ill or on a journey must fast an equal number of other days.” [al-Baqarah: 184]
He thus permitted the traveller to refrain from fasting in Ramadan to preserve his health, lest fasting and the hardship of travel together tax his strength, weakening him and impairing his health (1).
Concerning the evacuation of harmful matter by shaving the head while in the consecrated state of pilgrimage, He said:
“Whoever among you is ill or has an ailment of the scalp must offer compensation by fasting, charity, or sacrifice.” [al-Baqarah: 196]
He thus permitted someone who is ill or has an ailment of the scalp, while in the consecrated state of pilgrimage, to shave his head, thereby evacuating the corrupt matter and noxious vapours (2) on which (3) lice breed—as happened to Ka'b ibn 'Ujrah (4)—or which cause him illness.
These three are the fundamental principles of medicine. For each category, He mentioned a cause (5) and an example, thereby drawing attention to His blessings upon His servants in similar cases: protecting them from what is harmful, preserving their health, and evacuating harmful matter from their bodies. This is out of mercy for His servants, kindness towards them, and compassion for them (6). He is the Most Compassionate, the Most Merciful (7).