Prophet Abraham was indeed a monotheistic prophet and this was manifested in all his conduct. Allah, therefore, says the following when describing him:{Verily, Ibrâhim (Abraham) was an Ummah (a leader having all the good righteous qualities), or a nation, obedient to Allah, Hanifa (i.e. to worship none but Allâh), and he was not one of those who were Al-Mushrikûn (polytheists, idolaters, disbelievers in the Oneness of Allâh, and those who joined partners with Allâh).}
(An-Nahl:120)He (pbuh) grew up among polytheists. Even his father was one of the idolaters, and carved and served the idols. Abraham argued with his father and people:{And (remember) when Ibrâhim (Abraham) said to his father Azar: “Do you take idols as âlihâ (gods)? Verily, I see you and your people in manifest error.”}
(Al-An’âm:74)With compelling arguments he firmly rejected their polytheistic ways. He looked at Allah’s ever so apparent signs.{“When the night covered him over with darkness he saw a star. He said: “This is my lord.” But when it set,”}
(Al-An’âm:76)That is: he saw how it set.{76. he said: “I like not those that set.” 77. When he saw the moon rising up,}
(Al-An’âm:76-77)That is: appearing in the horizon, and he saw that some people worshipped it. he said:{“This is my lord.”}
(Al-An’âm:77)Condemning their actions, astonished by their worship!! Taking the opportunity, he said:{But when it set}
(Al-An’âm:77)That is: disappeared below the horizon. He went to the people and said:{77. He said: “Unless my Lord guides me, I shall surely be among the erring people.”78. When he saw the sun rising up}
(Al-An’âm:77-78)He saw how the people were worshipping it. He said:{“This is my lord. This is greater.”}
(Al-An’âm:78)Condemning their actions!! Astonished at how they made a god out of the sun?!{But when it set}
(Al-An’âm:78)and subsequently disappeared from sight. He went to those who were worshipping it and said to them:{78. O my people! I am indeed free from all that you join as partners in worship with Allâh. 79. Verily, I have turned my face towards Him Who has created the heavens and the earth Hanifa (Islâmic Monotheism, i.e. worshipping none but Allâh Alone) and I am not of Al-Mushrikûn (see V.2:105)”.}
(Al-An’âm:78-79)
source: islamkingdom