The word(s) "had" appears 413 time(s) in 356 verse(s) in Quran in Mohsin Khan translation.

(301) When the Messengers came to them, from before them and behind them (saying): "Worship none but Allah", they said: "If our Lord had so willed, He would surely have sent down the angels. So indeed we disbelieve in that with which you have been sent."

(302) And We have assigned for them (devils) intimate companions (in this world), who have made fair-seeming to them, what was before them (evil deeds which they were doing in the present worldly life and disbelief in the Reckoning and the Resurrection) and what was behind them (denial of the matters in the coming life of the Hereafter as regards punishment or reward). And the Word (i.e. the torment) is justified against them as it was justified against those who were among the previous generations of jinn and men that had passed away before them. Indeed they (all) were the losers.

(303) And if We had sent this as a Qur'an in a foreign language (other than Arabic), they would have said: "Why are not its verses explained in detail (in our language)? What! (A Book) not in Arabic and (the Messenger) an Arab?" Say: "It is for those who believe, a guide and a healing. And as for those who disbelieve, there is heaviness (deafness) in their ears, and it (the Qur'an) is blindness for them. They are those who are called from a place far away (so they neither listen nor understand)."

(304) And indeed We gave Musa (Moses) the Scripture, but dispute arose therein. And had it not been for a Word that went forth before from your Lord, (the torment would have overtaken them) and the matter would have been settled between them. But truly, they are in grave doubt thereto (i.e. about the Qur'an). [Tafsir Al-Qurtubi].

(305) And if Allah had willed, He could have made them one nation, but He admits whom He wills to His Mercy. And the Zalimun (polytheists and wrong-doers) will have neither a Wali (protector or guardian) nor a helper.

(306) And they divided not till after knowledge had come to them, through (selfish) transgression between themselves. And had it not been for a Word that went forth before from your Lord for an appointed term, the matter would have been settled between them. And verily, those who were made to inherit the Scripture [i.e. the Taurah (Torah) and the Injeel (Gospel)] after them (i.e. Jews and Christians) are in grave doubt concerning it (i.e. Allah's true religion - Islam or the Qur'an).

(307) Or have they partners with Allah (false gods) who have instituted for them a religion which Allah has not ordained? And had it not been for a decisive Word (gone forth already), the matter would have been judged between them. And verily, for the Zalimun (polytheists and wrong-doers) there is a painful torment.

(308) And they said: "If it had been the Will of the Most Gracious (Allah), we should not have worshipped them (false deities)." They have no knowledge whatsoever of that. They do nothing but lie!

(309) Say (O Muhammad صلى الله عليه و سلم): "If the Most Gracious (Allah) had a son (or children as you pretend), then I am the first of Allah's worshippers [who deny and refute this claim of yours (and the first to believe in Allah Alone and testify that He has no children)]." [Tafsir At-Tabari].

(310) Then they had turned away from him (Messenger Muhammad صلى الله عليه و سلم) and said: (He is) one taught (by a human being), a madman!"