Prophets were sent with Tawheed
Allaah Ta’ala said:
وَلَقَدْ بَعَثْنَا فِي كُلِّ أُمَّةٍ رَّسُولاً أَنِ اعْبُدُواْ اللّهَ وَاجْتَنِبُواْ الطَّاغُوتَ
And verily, We have sent among every Ummah a Messenger proclaiming: “Worship Allah (Alone), and keep away from Taghut (all false deities, etc. do not worship Taghut besides Allah).”
[Surah An-Nahl 36]