The Quran

وَلَقَد بَعَثنا في كُلِّ أُمَّةٍ رَسولًا أَنِ اعبُدُوا اللَّهَ وَاجتَنِبُوا الطّاغوتَ ۖ فَمِنهُم مَن هَدَى اللَّهُ وَمِنهُم مَن حَقَّت عَلَيهِ الضَّلالَةُ ۚ فَسيروا فِي الأَرضِ فَانظُروا كَيفَ كانَ عاقِبَةُ المُكَذِّبينَ

Muhammad Asad

And indeed, within every community¹ have We raised up an apostle [entrusted with this message]: "Worship God, and shun the powers of evil!"² And among those [past generations] were people whom God graced with His guidance,³ just as there was among them [many a one] who inevitably fell prey to grievous error:⁴ go, then, about the earth and behold what happened in the end to those who gave the lie to the truth!

Or "at every period", since the term ummah has this significance as well. In its wider sense, it may also be taken here to denote "civilization", thus comprising a human groupment as well as a period of time.
For this rendering of the term at-taghat, see surah 2, note 250. It is to be borne in mind that, in Qur'anic terminology, "worship of God" invariably implies the concept of man's sense of responsibility before Him: hence, the above commandment comprises, in the most concise formulation imaginable, the sum-total of all ethical injunctions and prohibitions, and is the basis and source of all morality as well as the one unchanging message inherent in every true religion.
I.e., who availed themselves of the guidance offered by Him to all human beings.
Lit., "upon whom error came to be inevitably established (haqqa 'alayhi)" or "against whom [a verdict of] error became inevitable": i.e., one whose heart "God has sealed" in consequence of his persistent, conscious refusal to submit to His guidance (see surah 2, note 7, as well as surah 14, note 4).