Al-Maeda: If Allah had Willed, He would have made you one nation, but that (He) may test you in what He has given you; so compete in good deeds. The return of you (all) is to Allah; Then He Will inform you about that in which you used to differ. (48)
Al-Room: And among His Signs is the creation of the heavens and the earth, and the difference of your languages and colours. Verily, in that are indeed signs for men of sound knowledge. (22)
Al-Hujraat: O mankind! We created you from a single (pair) of a male and a female, and made you into nations and tribes, that ye may know each other (not that ye may despise each other). Verily the most honoured of you in the sight of Allah is (he who is) the most righteous of you. And Allah has full knowledge and is well acquainted (with all things). (13)