I've been teaching Kierkegaard's Fear and Trembling recently in Istanbul. One advantage of teaching that text in a Muslim country, is that everyone is familiar with the story of Abraham and Isaac.
For those who don't know it, for Jews and Christians, it is the story in Genesis 22 of Abraham commanded to kill his son Isaac by God. Abraham takes Isaac to the place of Sacrifice, but God relieves him of the sacrifice by revealing a sheep for a substitute sacrifice. Sura 37 of the Koran refers to Abraham/Ibrahim nearly sacrificing his son, which is often interpreted by Muslims as referring to Ishmael rather than Isaac/Isak; and it refers to a great sacrifice rather than a specfic animal but it is always understood as a goat or sheep.
In any case, the story is very familiar because one of the major Muslim festivals is the Sacrifice Festival, which started on the 20th December this year. The Sacrifice Festival includes the ritual sacrifice of sheep, goats, and bulls to commemorate İbrahim's obedience and Allah's offer of the sheep as substitute.
From Kierkegaard's point of view the Koran story is significantly different from the version because Ibrahim tells his son of a vision of the sacrifice, and the son is willing to be sacrificed, so the trial is just as much of the son as the father. Kierkegaard emphasises Abraham no telling Isaac, as part of the emphasis on the silence appropriate to the absurd dialectic, the paradox of faith. The tragic hero may explain the problem, but not the Knight of faith.
Even if Kierkegaard had incorporated the Muslim account, I don't think it would have been too much of a problem. Fear and Trembling includes an account of different possible stories to fill in the very sketchy original story. The possibility that the son is Ishmael not Isaac, and that the son knows of the sacrifice would not change the factors Kierkegaard discusses. It would still be a miraculous son of Abraham's old age, and it could still be the case that Abraham did not tell his wife Sarah (mother of Isaac) of his servant Hagar (mother of Ishmael). Kierkegaard makes up the supposed silence of Abraham anyway, and if the silence was directed towards the mother that would fit with the various painful love stories Kierkegaard brings into Fear and Trembling in comparison with Abraham's story.