3GPP 24.501 v20.0.0 — the document's own text
5.6.1.3 Common procedure initiation
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
Upon receipt of the SERVICE REQUEST or CONTROL PLANE SERVICE REQUEST message, the AMF may initiate the common procedures e.g. the 5G AKA based primary authentication and key agreement procedure or the EAP based primary authentication and key agreement procedure.