The prophet referred to as as-Siddiq, “the truthful,” in the Qur’an is Yusuf (Joseph).
In Qur’an 12:46, a fellow prisoner addresses Yusuf as “Yusuf, O most truthful one” while asking him to interpret a dream. The Arabic word siddiq conveys exceptional truthfulness, sincerity, and steadfast faith. Muslim tradition therefore associates Yusuf with the honorific as-Siddiq, reflecting his integrity throughout the trials described in Surah Yusuf.
Yusuf’s story includes betrayal by his brothers, abandonment in a well, enslavement in Egypt, imprisonment after resisting temptation, and eventual elevation to authority. His ability to interpret dreams becomes the means by which he is released and appointed to manage Egypt’s storehouses during a coming famine. The Qur’an presents his moral restraint and forgiveness as central virtues.
A common mix-up is Abu Bakr, who is also famously called al-Siddiq in Islamic history. That title belongs to Abu Bakr as a companion of Muhammad, while Yusuf is the prophet associated with siddiq in Qur’an 12:46. Isa, Musa, and Ibrahim have other important titles and descriptions.