Surah 40. Ghafir, Ayah 34

Thus not only refusing to acknowledge Joseph's prophethood, but also denying the possibility of any prophet being sent by God (Zamakhshari). It would seem that Joseph had been accepted in Egypt as a prophet only by the ruling class, the Hyksos, who were of Arab origin; spoke a language closely related to Hebrew (cf. surah {12}, note [44]), and were, therefore, emotionally and culturally predisposed towards the spirit of Joseph's mission, while the rest of the population was and remained hostile to the faith preached by him.

 Meaning, your ancestors, because Joseph (ﷺ) died over 400 hundred years before Moses (ﷺ).

So far he has been speaking of general religious tradition. Now, as an Egyptian, addressing Egyptians, he refers to the mission of Joseph in Egypt, for which see the whole of Sura xii. Joseph was not born in Egypt, nor was he an Egyptian. With what wonderful incidents he came into Egypt! What difficulties did he not surmount among his own brothers first, and in the Egyptian family which afterwards adopted him! How injustice, spite, and forgetfullness on the part of others, yet wove a spell round him and made him a ruler and saviour of Egypt in times of famine! How he preached to prisoners in prison, the wife of 'Aziz in her household, to the Egyptian ladies in their banquet, and to the Court of Pharaoh generally. The Egyptians profited by the material gains which came to them through him, but as a nation remained sceptical of his spiritual truths for many generations after him.

The interval between Joseph and Moses was about one to three centuries, a very short period for the memory of a learned nation like the Egyptians. And yet they as a nation ignored his spiritual work, and afterwards even persecuted Israel in Egypt until Moses delivered them. They actually saw the benefits conferred by Joseph, but did not realise that Allah's Kingdom works continuously even though men ignore it.