The Quran

قالوا يا صالِحُ قَد كُنتَ فينا مَرجُوًّا قَبلَ هٰذا ۖ أَتَنهانا أَن نَعبُدَ ما يَعبُدُ آباؤُنا وَإِنَّنا لَفي شَكٍّ مِمّا تَدعونا إِلَيهِ مُريبٍ

Muhammad Asad

They answered: "O Salih! Great hopes did we place in thee ere this!¹ Wouldst thou forbid us to worship what our forefathers were wont to worship? Because [of this], behold, we are in grave doubt, amounting to suspicion, about [the meaning of] thy call to us!"²

Lit., "Thou wert among us one in whom hope was placed ere this": an allusion to Hud's outstanding intellect and strength of character, which had probably caused his tribe to see in him their future leader - until he startled them by his passionate demand that they should abandon their traditional beliefs and devote themselves to the worship of the One God.
Lit., "we are indeed in disquieting doubt as to that to which thou invitest us". It is to be borne in mind that the pre-Islamic Arabs regarded their gods, as well as the angels (whom they believed to be "God's daughters"), as legitimate mediators between man and God, whose existence as such they did not deny; consequently, they were greatly disturbed by their prophet's demand that they should abandon the worship of those allegedly divine or semi-divine beings. The above answer of the Thamud seems to imply that they might consider Salih's claim to be a prophet more favourably if he would but refrain from insisting that "you have no deity other than Him": a suggestion that fully explains Salih's retort in the next verse.