Sunan an-Nasa’i 2317
The Book of Fasting
Interpreting the saying of Allah, The Mighty And Sublime: "And as for those who can fast with difficulty,(e.g. an old man), they have (a choice either to fast or) to feed a Miskin (poor person) (for every day)"
It was narrated from 'Ata from Ibn 'Abbas: concerning this verse "And as for those who can fast with difficulty, (a choice either to fast or) to feed a Miskin (poor person) (for every day)." That for those who can fast with difficulty means they find it hard; to feed a Miskin means feeding one poor person for each day. But whoever does good of his own accord means feeding another poor person. This is not abrogated, and it is bette for him. And: that "you fast is better for you" means there is no concession regarding this except for those who are not able to fast, or who are incurably sick.