´It was narrated from Abu Umamah that he asked the Messenger of Allah:` "Which deed is best?" he said: "Take to fasting, for there is nothing equal to it."
Explanation & Benefits
Hafiz Muhammad Ameen
The narrator of this tradition is titled "Da‘eef" (weak), not because the narration itself is weak, but because he had become physically weak due to excessive worship.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 2224