The Quran

أَلَم يَأتِكُم نَبَأُ الَّذينَ مِن قَبلِكُم قَومِ نوحٍ وَعادٍ وَثَمودَ ۛ وَالَّذينَ مِن بَعدِهِم ۛ لا يَعلَمُهُم إِلَّا اللَّهُ ۚ جاءَتهُم رُسُلُهُم بِالبَيِّناتِ فَرَدّوا أَيدِيَهُم في أَفواهِهِم وَقالوا إِنّا كَفَرنا بِما أُرسِلتُم بِهِ وَإِنّا لَفي شَكٍّ مِمّا تَدعونَنا إِلَيهِ مُريبٍ

Muhammad Asad

HAVE THE STORIES of those [deniers of the truth] who lived before you never yet come within your ken - [the stories of] the people of Noah, and of [the tribes of] 'Ad and Thamud, and of those who came after them? None knows them [now] save God.¹ There came unto them their apostles with all evidence of the truth - but they covered their mouths with their hands² and answered: "Behold, we refuse to regard as true the message with which you [claim to] have been entrusted; and, behold, we are in grave doubt, amounting to suspicion, about [the meaning of] your call to us!"³

I.e., they have disappeared from the face of the earth, and none save God knows today how many they were and how they lived. See verse 14 and note 18 below.
Lit., "they put their hands into their mouths" - an idiomatic phrase indicating one's inability to refute a reasonable proposition by cogent, logical counter-arguments: for the out-of-hand rejection of the apostles' message by their recalcitrant compatriots cannot by any means be regarded as an "argument".
See surah 11, note 92. It is to be noted that whereas in 11:62 this reply is placed in the mouth of people of one particular community - the Thamud - and is phrased in the singulaar ("thy call to us"), it appears here in the plural ("your call to us") and represents the gist of the answers given by various communities to various prophets. This generalization, underlying the entire subsequent account and containing echos of several Qur'anic narratives relating to the experiences of individual apostles of earlier times, is obviously meant to bring out the symptomatic character of the attitude referred to: the stubborn attitude of people who either deny God altogether, or - while not consciously denying His existence - yet feel compelled to interpose all manner of imaginary "mediators" (thought to be divine or semi-divine) between themselves and Him, thus denying, by implication, His omniscience and omnipotence.