The ontological argument, as an a priori argument for the existence of God, had attracted the attention of Islamic philosophers prior to Anselm and became renowned as the Burhān al-Ṣiddīqīn (the Proof of the Truthful). The Burhān al-Ṣiddīqīn maintains that God's existence can be established through reflection upon existence itself, without recourse to the acts and creatures of the Necessary Being (Wājib al-Wujūd) and without relying on philosophical premises. Is the Burhān al-Ṣiddīqīn truly independent of philosophical and cosmological foundations and premises? Is it not based upon the principles of causality and the impossibility of circularity and infinite regress? How are these foundations and premises obtained? Are they not derived from the observation, experience, and analysis of the world other than God and His creatures? According to Avicenna's definition, however, the method of the Truthful was not supposed to employ creatures as intermediaries. Moreover, does this necessity and ontological requirement establish the very God affirmed by the revealed religions? Can every human being arrive at God merely from the proposition that “existence admits of no non-existence and is necessary”? The aim of this article is to critically examine the most significant formulations of the Burhān al-Ṣiddīqīn presented by Islamic philosophers in their proofs for the existence of God. This study adopts an analytical-critical method through an examination of the writings of al-Fārābī, Avicenna (Ibn Sīnā), Mullā Ṣadrā, Allāmeh Ṭabāṭabāʾī, and their commentators. As this paper demonstrates, the principal formulations of the Burhān al-Ṣiddīqīn make use of philosophical and cosmological foundations and premises, even when such premises are not explicitly stated but remain implicit. Nevertheless, it must be acknowledged that these arguments may be regarded as sound, useful, and defensible demonstrations for establishing the existence of God, though not as a complete deductive proof, since some of their premises remain open to dispute.