On the authority of Abū ‘Umāmah (may Allāh be pleased with him) who said:
I said, “O Messenger of Allāh order me with an action.” He said, “Take to fasting because verily there is nothing equal to it.” I said, “O Messenger of Allāh order me with an action.” He replied, “Take to fasting because verily there is nothing equal to it.”
Shaykh Al-Albāni (may Allāh have mercy upon him) mentioned (Ṣaḥīḥ At-Targhīb wa At-Tarhīb, 2000, p.580) that it was reported in Nasāi’, Ibn Khuzaymah (in his Ṣaḥīḥ) with the repetition as is mentioned, and also without it, and Ḥākim who authenticated it. And the narration in Nasāi’ mentions that he (Abū ‘Umāmah) said:
I came to the Messenger (sallAllāhu 'alayhi wa sallam) and said, “O Messenger of Allāh! Order me with an affair by which Allāh will benefit me.” He replied, ‘Take to fasting because there is nothing like it”
And it was reported by Ibn Ḥibbān (in his Ṣaḥīḥ) in a narration that he (Abū ‘Umāmah) said:
“I said O Messenger of Allāh direct me to an action by which I may enter paradise.” He replied, “Take to fasting because there is nothing like it.”
He said: “And Abū ‘Umāmah used to be as such that no smoke used to be seen from his house during the daytime except if they had guests.”
[All the above narrations were graded Ṣaḥīḥ by Shaykh Al-Albāni (Ṣaḥīḥ At-Targhīb wa At-Tarhīb, 2000, p.580)]