From the Nabataean letter 𐢙 (ṣ, “ṣade”), derived from the Phoenician letter 𐤑 (ṣ, “ṣade”), from an uncertain Egyptian hieroglyph (𓇑?). See also ܨ (ṣ, “ṣade”), צ (ts, “tsadi”), Cyrillic Ц.
Practice speaking and memorizing "ص" and many other words and sentences in Arabic.