Definition of (As-Salaf) : Ibn Faris (d. 395 H.) states: "The (letter) Sin, the (letter) Lam, and (letter) Fa (together), is a root which indicates precedence and antecedence. A derivation of this root is "as-salaf" which means those who have passed on. (1) And the Salaf ...are the predecessors.(2)
(1) Maqayis Al-Lugha by Ibn Faris, the root: Salaf.
(2) Lisan Al-Arab by Ibn Mandhur, the root: Salaf.