the Messenger of Allah said, concerning one who fasted for the rest of his life: "He neither fasted nor broke his fast." 'Ata said: "someone who heard him told me that Ibn 'Umar (said) that the Prophet said: 'Whoever fasts every day of his life, then he has not fasted."
The Book of Fasting - Sunan an-Nasa'i 2381
The Messenger of Allah said, concerning one who fasted for the rest of his life: "He neither fasted nor broke his fast." 'Ata said: "someone who heard him told me that Ibn 'Umar (said) that the Prophet said: 'Whoever fasts every day of his life, then he has not fasted."
Scholarly Commentary
This hadith establishes the prohibition against perpetual fasting, which contradicts the balanced nature of Islamic worship. The phrase "he has not fasted" indicates such continuous fasting lacks religious validity and reward.
The wisdom behind this prohibition includes: preserving physical health, maintaining social obligations, observing Islamic festivals, and following the Sunnah of periodic breaking of fast. Islam encourages moderation in all acts of worship.
Scholars explain that valid fasting requires both observance and breaking of fast according to Islamic guidelines. Perpetual fasting resembles monasticism, which Islam rejects in favor of balanced devotion within worldly life.
Legal Rulings
The majority of scholars consider perpetual fasting makruh (disliked) rather than haram (forbidden), except for those who practice the recommended fasts of Dawud (alternate days) which maintain balance.
Exceptions exist for voluntary fasts like Mondays and Thursdays, the white days (13th, 14th, 15th of lunar month), and six days of Shawwal - provided one breaks fast on Eid and other prohibited days.