Reference: Fataawa Ramadhaan – Volume 2, Pages 672-673, Fatwa No.675
Fataawa wa Rasaa.il Muhammad ibn Ibraaheem Aal ash-Shaykh – Volume 4, Page 205
Question: Regarding the one who fasts every other day, is that correct?
Response: Fasting every other day is the best of fasts, for that which has been narrated on the authority of ‘Umar ibn al-Khattaab (radhi-yAllaahu ‘anhu) that the Prophet (sal-Allaahu ‘alayhi wa sallam) said:
However, that is only for he who is able to do so continuously. As for the person who is unable to do so, then he should maintain continuity in that which he is able, since it has been mentioned in a hadeeth that he (sal-Allaahu ‘alayhi wa sallam) said: