Allah said,

﴿وَإِلَى ثَمُودَ﴾

(And to Thamud), meaning, to the tribe of Thamud, We sent their brother Salih,

﴿قَالَ يَاقَوْمِ اعْبُدُواْ اللَّهَ مَا لَكُمْ مِّنْ إِلَـهٍ غَيْرُهُ﴾

(He said: "O my people! Worship Allah! You have no other god but Him.'') All Allah's Messengers called to the worship of Allah alone without partners. Allah said in other Ayat,

﴿وَمَآ أَرْسَلْنَا مِن قَبْلِكَ مِن رَّسُولٍ إِلاَّ نُوحِى إِلَيْهِ أَنَّهُ لا إِلَـهَ إِلاَّ أَنَاْ فَاعْبُدُونِ ﴾

(And We did not send any Messenger before you but We revealed to him (saying): "None has the right to be worshipped but I, so worship Me.'') ﴿21:25﴾ and,

﴿وَلَقَدْ بَعَثْنَا فِى كُلِّ أُمَّةٍ رَّسُولاً أَنِ اعْبُدُواْ اللَّهَ وَاجْتَنِبُواْ الْطَّـغُوتَ﴾

(And verily, We have sent among every Ummah a Messenger (proclaiming): "Worship Allah (Alone), and avoid Taghut (all false deities)'') ﴿16:36﴾.