God has Moses feel his own breast/hand and it turns leprous, then is restored, as a sign to convince Israel Moses was sent by God (Exodus 4:6-7).

Exodus 4 gives Moses three signs (staff-to-serpent, hand-to-'leprosy', water-to-blood) because Moses keeps objecting (4:1, 8, 9) — the multiplication of signs is patient accommodation to a reluctant prophet, not divine caprice, and the pattern matches the wider ANE/biblical prophetic-call genre of reluctance-plus-attesting-sign (Gideon, Judges 6; Isaiah 6; Jeremiah 1). Hebrew tsara'ath (rendered 'leprosy' in the KJV) is a broad term (BDB, HALOT) for various scaling skin conditions, not specifically Hansen's disease — a real translation imprecision, but it does not change the narrative's logic. Crucially, the text later draws a deliberate contrast between this sign and pagan magic: Egypt's court magicians can mimic some plagues via their 'secret arts' (Exod 7:11, 22; 8:7) but cannot replicate or cure others, prompting even them to confess 'this is the finger of God' (8:18-19). Moses' sign requires no incantation, ritual formula, or learned technique — only obedience — marking it as an act of divine fiat rather than manipulative magic. The tsara'ath/cleansing motif recurs meaningfully later (Miriam, Num 12:10-15; Naaman, 2 Kings 5), tying this sign into a larger canonical theme of God's authority over impurity and restoration.

God's willingness to grant a fearful, repeatedly doubting prophet multiple concrete, empirical signs (rather than simply commanding blind assent) shows a pattern of covenantal condescension and pedagogical patience running through the whole canon — Gideon's fleece, Elijah at Horeb, Thomas invited to touch the wounds (John 20:27) — a God who meets creaturely weakness with evidence rather than contempt.