In Islam, the idea of Allah having partners (i.e., the Trinity), is a lie. To associate partners with Allah is an unforgivable sin. The Quran teaches that the Trinity is three gods (Surah 4:171), even though that is not what it actually is according to Christianity. Islam misrepresents the Christian perspective.  The Trinity is not three gods. Nevertheless, Muhammad’s teachings in the Quran routinely deny that Allah has partners (polytheism) and taught that ascribing God is a Trinity is an unforgivable sin.

1. Allah does not forgive that you set up partners with him
   1. Surah 4:48, “Allah forgiveth not that partners should be set up with Him; but He forgiveth anything else, to whom He pleaseth; to set up partners with Allah is to devise a sin Most heinous indeed.”
   2. Surah 4:116, “Allah forgiveth not (The sin of) joining other gods with Him; but He forgiveth whom He pleaseth other sins than this: one who joins other gods with Allah, Hath strayed far, far away (from the right).”
   3. Surah 11:55, “Other gods as partners! So scheme (your worst) against me, all of you, and give me no respite.”
2. Associate no partners with Allah
   1. Surah 3:64, “Say: “O People of the Book! Come to common terms as between us and you: That we worship none but Allah; that we associate no partners with him; that we erect not, from among ourselves, Lords and patrons other than Allah.” If then they turn back, say ye: “Bear witness that we (at least) are Muslims (bowing to Allah’s Will).”
   2. Surah 4:36, “Serve Allah, and join not any partners with Him; and do good—to parents, kinsfolk, orphans, those in need, neighbors who are near, neighbors who are strangers, the companion by your side, the wayfarer (ye meet), and what your right hands possess: For Allah loveth not the arrogant, the vainglorious.”
   3. Surah 6:162-163, “Say: “Truly, my prayer and my service of sacrifice, my life, and my death, are (all) for Allah, the Cherisher of the Worlds. 163 No partner hath He: this am I commanded, and I am the first of those who bow to His will.”
   4. Surah 13:36, “Those to whom We have given the Book rejoice at what hath been revealed unto thee: but there are among the clans those who reject a part thereof. Say: “I am commanded to worship Allah, and not to join partners with Him. Unto Him do I call, and unto Him is my return.”
3. Associating partners with Allah is a lie
   1. Surah 10:66, “Behold! Verily to Allah belong all creatures, in the heavens and on earth. What do they follow who worship as His “partners” other than Allah? They follow nothing but fancy, and they do nothing but lie.“
4. Associating partners with Allah is a sin
   1. Surah 11:54-55, “We say nothing but that (perhaps) some of our gods may have seized thee with imbecility.” He said: “I call Allah to witness, and do ye bear witness, that I am free from the sin of ascribing, to Him, 55 “Other gods as partners! So scheme (your worst) against me, all of you, and give me no respite.”
   2. Surah 22:31, “Being true in faith to Allah, and never assigning partners to Him: if anyone assigns partners to Allah, is as if he had fallen from heaven and been snatched up by birds, or the wind had swooped (like a bird on its prey) and thrown him into a far-distant place.”
   3. Surah 42:21, “What! Have they partners (in godhead), who have established for them some religion without the permission of Allah? Had it not been for the Decree of Judgment, the matter would have been decided between them (at once). But verily the Wrong-doers will have a grievous Penalty.”
5. Forbidden to associate partners with Allah
   1. Surah 7:33, “Say: the things that my Lord hath indeed forbidden are: shameful deeds, whether open or secret; sins and trespasses against truth or reason; assigning of partners to Allah, for which He hath given no authority; and saying things about Allah of which ye have no knowledge.”
6. Other
   1. Surah 6:78-79, “When he saw the sun rising in splendour, he said: “This is my Lord; this is the greatest (of all).” But when the sunset, he said: “O my people! I am indeed free from your (guilt) of giving partners to Allah. 79 “For me, I have set my face, firmly and truly, towards Him Who created the heavens and the earth, and never shall I give partners to Allah.”
   2. Surah 9:31, “They take their priests and their anchorites to be their lords in derogation of Allah, and (they take as their Lord) Christ the son of Mary; yet they were commanded to worship but One Allah: there is no god but He. Praise and glory to Him: (Far is He) from having the partners they associate (with Him).
   3. Surah 17:111, “Say: “Praise be to Allah, who begets no son, and has no partner in (His) dominion: Nor (needs) He any to protect Him from humiliation: yea, magnify Him for His greatness and glory!”
7. Trinity
   1. Is Blasphemy
      1. Surah 5:73, “They do blaspheme who say: Allah is one of three in a Trinity: for there is no god except One Allah. If they desist not from their word (of blasphemy), verily a grievous penalty will befall the blasphemers among them.”
   2. Mary part of the Trinity?
      1. Surah 5:116, “And behold! Allah will say: “O Jesus the son of Mary! Didst thou say unto men, worship me and my mother as gods in derogation of Allah?” He will say: “Glory to Thee! Never could I say what I had no right (to say). Had I said such a thing, thou wouldst indeed have known it. Thou knowest what is in my heart, Thou I know not what is in Thine. For Thou knowest in full all that is hidden.”
   3. Say not trinity
      1. Surah 4:171, “O People of the Book! Commit no excesses in your religion: Nor say of Allah aught but the truth. Christ Jesus the son of Mary was (no more than) an apostle of Allah, and His Word, which He bestowed on Mary, and a spirit proceeding from Him: so believe in Allah and His apostles. Say not “Trinity”: desist: it will be better for you: for Allah is one Allah: Glory be to Him: (far exalted is He) above having a son. To Him belong all things in the heavens and on earth. And enough is Allah as a Disposer of affairs.”