In the name of Allaah, the Most Merciful, the Bestower of Mercy. All praise is due to Allaah, the Lord of the all that exists. And may the peace and blessings be upon our Messenger Muhammad and upon his family and his companions. To proceed:
The correctness of aqeedah is the (most) fundamental principle. This is because bearing witness that Laa Ilaaha Illa Allaah Wa Anna Muhammaddan Rasool Allaah (there is no deity worthy of worship except Allaah and that Muhammad is His Messenger), is the first pillar of Islaam. And the Messengers called firstly, to the correction of the aqeedah because all acts of worship and behavior depends on it and without the correct aqeedah, there is no benefit from (these) deeds. The Most High said: “But if they had joined in worship others with Allaah, all that they used to do would have been of no benefit to them.” - Al-An’am (6):88
And their deeds became invalid.
And Allaah (سبحانه وتعالى) said: “Verily, whosoever sets up partners in worship with Allaah, then Allaah has forbidden Paradise for him, and the Fire will be his abode. And for the Dhaalimoon (polytheists and wrong-doers) there are no helpers.” - Al-Maa’idah (5):72
And the Most High said: “And indeed it has been revealed to you (O Muhammad (صلى الله عليه وسلم)), as it was to those (Allaah’s Messengers) before you: ‘If you join others in worship with Allaah, (then) surely (all) your deeds will be in vain, and you will certainly be among the losers.’” - Az-Zumar (39):65
From these texts and other than them, it is clear that the correction of the aqeedah is from the important (affairs) and at the forefront of the da’wah. And the first (affair) to establish for the da’wah is the correction of aqeedah. And the Prophet (صلى الله عليه وسلم) remained in Makkah for thirteen years after his mission began, calling the people to the correction of the aqeedah and to at-Tawheed. And the faraa’id (obligatory acts of worship) were not revealed to him except in Madeenah.
Yes, and the salaat was made obligatory upon him in Makkah before the hijrah and the rest of the shar’iah was imposed on him after the hijrah. From this we have evidence that deeds are not accepted except after the correction of the aqeedah.
And this is for the one who says: That the eemaan is sufficient without having interest for the aqeedah.
This is contradictory because eemaan is not eemaan except if the aqeedah is correct. And if the aqeedah is not correct, then there is no eemaan, and (there is) no deen (religion).