The word(s) "warn" appears 143 time(s) in 129 verse(s) in Quran in Saheeh International translation.

(1) Indeed, those who disbelieve - it is all the same for them whether you warn them or do not warn them - they will not believe.

(2) Indeed, We have sent you, [O Muhammad], with the truth as a bringer of good tidings and a warner, and you will not be asked about the companions of Hellfire.

(3) Mankind was [of] one religion [before their deviation]; then Allah sent the prophets as bringers of good tidings and warners and sent down with them the Scripture in truth to judge between the people concerning that in which they differed. And none differed over the Scripture except those who were given it - after the clear proofs came to them - out of jealous animosity among themselves. And Allah guided those who believed to the truth concerning that over which they had differed, by His permission. And Allah guides whom He wills to a straight path.

(4) Let not believers take disbelievers as allies rather than believers. And whoever [of you] does that has nothing with Allah, except when taking precaution against them in prudence. And Allah warns you of Himself, and to Allah is the [final] destination.

(5) The Day every soul will find what it has done of good present [before it] and what it has done of evil, it will wish that between itself and that [evil] was a great distance. And Allah warns you of Himself, and Allah is Kind to [His] servants."

(6) [We sent] messengers as bringers of good tidings and warners so that mankind will have no argument against Allah after the messengers. And ever is Allah Exalted in Might and Wise.

(7) O People of the Scripture, there has come to you Our Messenger to make clear to you [the religion] after a period [of suspension] of messengers, lest you say, "There came not to us any bringer of good tidings or a warner." But there has come to you a bringer of good tidings and a warner. And Allah is over all things competent.

(8) [Be warned of] the Day when Allah will assemble the messengers and say, "What was the response you received?" They will say, "We have no knowledge. Indeed, it is You who is Knower of the unseen"

(9) Say, "What thing is greatest in testimony?" Say, "Allah is witness between me and you. And this Qur'an was revealed to me that I may warn you thereby and whomever it reaches. Do you [truly] testify that with Allah there are other deities?" Say, "I will not testify [with you]." Say, "Indeed, He is but one God, and indeed, I am free of what you associate [with Him]."

(10) And We send not the messengers except as bringers of good tidings and warners. So whoever believes and reforms - there will be no fear concerning them, nor will they grieve.