An important excerpt from Sh. Ayman ath-Thawahiri's letter to Sh. Abu Mus'ab az-Zarqawi:

“Striving for the (gain of the) scholars: From the angle of not highlighting the doctrinal differences which the masses do not understand, such as this one is Maturidi or this one is Ash’ari or this one is Salafi, and from the angle of doing justice to the people, for there may be among the people an innovation or a shortcoming, but on the other hand they may have something to offer in jihad, fighting and sacrificing in the cause of Allah. We have seen amazing examples in the Afghan jihad, and the commander of the believers, Mullah Muhammad 'Umar (may Allah protect him) himself is a Hanafi adherent and Maturidi in doctrine, but he stood in the history of Islam with a stance rarely taken by others.

[…]

The scholars among the masses are, as well, the symbol of Islam and its slogan. Their disparagement may lead to the general public deeming the religion and its adherents as being unimportant. This is a greater harm than the benefit of criticizing a scholar on an innovation or an issue (differed on). Of course, these words of mine have nothing to do with the hypocritical traitors allied to the crusaders, but I wish to stress against diminishing the scholars before the masses.

Also, the active mujahideen scholars - even if there may be some innovation or shortcoming in them not amounting to disbelief - we must find a means to include them and to benefit from their abilities. You know better than for me to remind to you- that many of the most active eminent scholars of Islam such as al-‘Izz bin AbdisSalam, an-Nawawi and Ibn Hajar (may Allah have mercy on them) were Ash’ari. And many of the most eminent figures of jihad, whom the Ummah agreed unanimously on their praiseworthiness such as Nuruddeen bin Zanki and Saluddeen al-Ayyubi, were Ash’ari. The mujahideen rulers who came after them - though not reaching their level - whom the scholars and the historians praised such as Sayfuddeen Qutuz, Ruknuddeen Baybars, an-Nasir Muhammad bin Qalawoon, and Muhammad al-Fatih, were Ash’ari or Maturidi. They fell into errors, sins, and innovations. The stances of Shaykhul Islam Ibn Taymiyyah regarding an-Nasir Muhammad bin Qalawoon, his praise of him and his inciting him to jihad - despite the trials and imprisonment which befell the Shaykh during his time - are well known.

If you take into account the fact that most of the Ummah's scholars are Ash’ari or Maturidi, and if you take into consideration as well the fact that the issue of correcting the mistakes of ideology is an issue that will require generations of da’wah and rectifying the educational curricula, and that the mujahideen are not able to undertake this burden, rather they are in need of those who will help them with the difficulties and problems they face; if you take all this into consideration, and add to it the fact that all Muslims are all addressed (to wage) jihad, whether they are Salafi or non-Salafi, then you would understand that it is a duty of the jihad movement to include the abilities of the Ummah and in its wisdom and prudence to fill the role of leader, trailblazer, and exploiter of all the capabilities of the Ummah for the sake of achieving our aims: a caliphate on the way of the Prophet, by Allah’s permission.

I do not know the details of the situation where you are, but I do not want us to repeat the mistake of Jameel ar-Rahman (al-Afghani), who was killed and whose organization was shattered, because he neglected the realities on the ground.”

[Excerpt taken from Sh. Ayman ath-Thawihiri’s letter to Sh. Abu Mus’ab az-Zarqawi in 2005]