A common view amongst sunnis is that Ibrahim’s father was indeed an idol worshipper. You can refer to their books of exegesis to see what they have said about this, e.g. Tabari, Ibn Kathir and Qurtubi for verse 14:41 amongst others. Those who hold this belief present the following verse as proof:
[9:114] And Ibrahim asking forgiveness for his Ab (father) was only owing to a promise which he had made to him; but when it became clear to him that he was an enemy of Allah, he declared himself to be clear of him; most surely Ibrahim was very tender-hearted forbearing.
On the other hand, Shias completely reject this, and believe that the line of Prophethood was pure and free from polytheism. So then how do we explain the above verse? Ayatollah Jawadi Amoli has answered this question is his tafsir:
هل كان والد النبي إبراهيم (عليه السلام) موحداً؟
إن عنوان «الأب» كما يطلق على الأب فإنه يطلق على غيره كالعمّ أيضاً، و هذا هو منشأ الترديد في قضية النبي إبراهيم من أن أبوه هل كان آزر عابد الوثن أم لا. فالذي يظهر من الآية
«و إذ قال إبراهيم لأبيه آزر أتتخذ أصناماً آلهة»(1)، و الآيات 42 من سورة مريم، و 52 من سورة الأنبياء، و 70 من سورة الشعراء، و 85 من سورة الصافات، و 26 من سورة الزخرف، و 114 من سورة التوبة و غيرها، أن أبا النبي إبراهيم لم يكن موحداً؛ أما أن هذا الأب هل هو نفس الوالد أم غيره، وهل أن والد النبي إبراهيم هل كان موحداً أم لا، فلا يمكن استظهار أي واحد من هذين المطلبين من الآيات المشتملة على عنوان «الأب»؛ و لكن يمكن استنباط كلا المطلبين من آية أخرى متضمنة لكلمة الوالد لا كلمة «الأب»؛ فيمكن معرفة أن آزر عابد الوثن لم يكن والد النبي إبراهيم، و أن الشخص الآخر الذي هو والد النبي إبراهيم و الذي لم يذكر اسمه في القرآن، كان موحداً، لا مشركاً؛ فقد قال الله:
أ- «و ما كان للنبي و الذين آمنوا أن يستغفروا للمشركين و لو كانوا أولي قربى»(2).
ب- «و ما كان استغفار إبراهيم لأبيه إلا عن موعدة وعدها إياه فلما تبيّن له أنه عدو لله تبرأ منه»(3)، أي لم يستغفر له بعد ذلك.
ج- قال النبي إبراهيم (عليه السلام) في دعاء له في عهد الكبر و في أواخر حياته: «ربنا اغفر لي و لوالديّ و للمؤمنين يوم يقوم الحساب»(4).
من هنا يمكن استنباط المطلبين المشار إليهما: أحدهما هو أن آزر عابد الوثن لم يكن والد النبي إبراهيم؛ لأنه تبرأ من آزر بعد أن تبين له شركه و عداؤه مع الله، و لم يستغفر له بعد ذاك، و المطلب الآخر أنه استغفر لوالديه في عهد الكبر، فيظهر أنهما كانا يستحقان الاستغفار؛ أي كانا كسائر المؤمنين من أهل الإيمان لا من أهل الشرك.
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1- سورة الأنعام، الآية 74.
2- سورة التوبة، الآية 113.
3- سورة التوبة، الآية 114.
4- سورة إبراهيم، الآية 41.
تسنيم (التسنيم)، ج 1، ص 117.
http://arabic.esraco.net/main.asp
Translation:
Question: Was the father of Prophet Abraham [as] a monotheist?
The word ‘Ab’ can refer to the biological father as well as to the uncle or others*. In the case of Prophet Abraham the question is whether Azar the idol worshipper was his biological father or not? What is apparent from the verse [6:74] ‘And when Abraham said to his Ab (father) do you take idols for gods?’ and verses 19:42, 21:52, 26:70, 37:85, 43:26, 9:114 and others is that the ‘Ab’ of Abraham [as] was not a monotheist. However it is unclear from these verses whether the ‘Ab’ was his actual biological father or someone else, and whether the biological father of Abraham was a monotheist or not. We are unable to come to any one of these conclusions from these verses that use the word ‘Ab’, but we are able to use another verse that uses the word ‘walid’ (biological father) instead of ‘Ab’ {which is a more general term} to give us the answers. From this verse (that uses walid) we come to know that Azar the idol worshipper was not the biological father of Prophet Abraham [as] but someone else who was a monotheist but whose name hasn’t been mentioned in the Qur’an. Allah swt has said:
(i) [9:113] It is not (fit) for the Prophet and those who believe that they should ask forgiveness for the polytheists, even though they should be near relatives, after it has become clear to them that they are inmates of the flaming fire.
(ii) [9:114] And Ibrahim asking forgiveness for his Ab was only owing to a promise which he had made to him; but when it became clear to him that he was an enemy of Allah, he declared himself to be clear of him; most surely Ibrahim was very tender-hearted forbearing.
(iii) Prophet Abraham [as] supplicated to Allah in his old age saying [14:41] Our Lord! Forgive me and my parents and believers on the day when the account is cast.
From these verses we can conclude two things. Firstly, Azar the idol worshipper was not the biological father of Prophet Abraham [as] as he ‘declared himself to be clear of him’ once it became evident that he was a polytheist and enemy of Allah swt, and he never asked forgiveness for him after that. Secondly, he sought forgiveness for his parents (walidaya) when he was an old man**, showing that they were worthy of forgiveness, i.e. they were believers and not polytheists.
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*As proof for this read verse 2:133 in which Nabi Isma’eel [a] who was Ya’qoob’s [a] paternal uncle is referred to as his Ab.
**We know that the prayer for forgiveness of his parents in 14:41 was said in Nabi Ibrahim’s [a] old age because he prays for his sons as well, and he had these sons when he was an old man. This is the whole passage:
[14:39] Praise be to Allah, Who has given me in old age Ismail and Ishaq; most surely my Lord is the Hearer of prayer:
[14:40] My Lord! make me keep up prayer and from my offspring, O our Lord, and accept my prayer
[14:41] Our Lord! Forgive me and my parents and believers on the day when the account is cast
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