Halal-screened equity, mostly.
Halal-screened ETFs and mutual funds
HLAL, SPUS, Amana, Azzad funds publish a per-share purification rate (typically <1%). Apply that rate to dividends received.
Individual halal-screened stocks
Companies that pass AAOIFI Standard 21 screening but have small interest income (e.g. Apple's cash holdings). Use the per-share purification rate from the screening provider.
Pure halal investments
Sukuk, Mudarabah-based investments, Islamic bank deposits. No purification needed; returns are entirely halal by structure.
When in doubt
Round up. Purification is meant to err on the side of generosity. The donation is to charity without intent of reward (no tax deduction-seeking, etc.).
Per MUFTI_CONTENT_POLICY.md, this methodology is editorial. A Mufti Saad signed methodology block replaces this when corpus content covers purification.