the Fatwa Department Research Committee - chaired by Sheikh `Abd al-Wahhâb al-Turayrî
The text you refer to is: “Being an Arab is not because of your father or mother, but being an Arab is on account of your tongue. Whoever learns Arabic is an Arab.”
This hadîth is related by Ibn`Asâkir in Târîkh Dimashq. It is a very weak hadîth. Ibn `Asâkir, al-Dhahabî and al-Nasâ’î declared its narrator, Salmân b. `Abd Allah to be extremely weak and unreliable.
Source: Islam Today