Q- Is it correct to attribute the following Hadith to our beloved Nabi (sallallahu ‘alayhi wasallam) ? “The person who acts upon what he knows, Allah Ta’ala will grant him knowledge of that which he does not know”?
These words have not been authentically recorded as that of Rasulullah (sallallahu ‘alayhi wasallam). (Tabaqatush Shafi’iyyah, vol.6 pg.290). The preferred view is that these are actually the words of Nabi ‘Isa (‘alayhis salam). (Hilyatul Awliya, vol.10 pg.13 and Fathul Mughith, vol.2 pg.126)
Sayyiduna Abud Darda (radiyallahu’anhu) is reported to have made a similar statement. (Al-Jami’u li Akhlaqir Rawi, no. 35). This subject matter is also found in the Quran, Allah Ta’ala says: ‘Fear Allah, and Allah will grant you knowledge.’ Surah Baqarah, Ayah: One who fears Allah is generally an upright, practicing individual. For this upright practice, he is rewarded with increase in knowledge.
Summary
The subject matter of this statement is indeed established, but to attribute these exact words in question to Nabi (sallallahu ‘alayhi wasallam) needs substantiation.
And Allah Ta’ala Knows Best