“These gatherings of ‘dhikr’ are in reality gatherings which Allāh has prohibited the People of Bidʿah from: these ‘Fuqarāʾ’ (i.e. the poor ones, which is a name Ṣufīs refer to themselves with) who claim that they traverse the path of Taṣawwuf. It is rare that you find one of them who proficiently recites the Fātiḥah in the prayer, except that he errs in it, in addition to doing the same in other Sūrahs. Likewise, he does not know how to worship, nor clean himself (al-Istinjāʾ) after relieving himself, or purify himself (from minor impurities) for prayer, or make ghusl (purifying himself from major ritual impurity).

How would they know these things, as they prohibit the gatherings of religious knowledge upon which Allāh’s Mercy descends? Likewise, tranquility descends upon them and the angels encompass them [i.e. those in the gatherings of religious knowledge].

Due to them [i.e. the Ṣūfīs] being blind to this light, they have been misguided and follow ignorant people like themselves. They began to read the aḥādīth of the Prophet (صلى الله عليه وسلم) and Qurʾānic verses and apply them according to their opinions, not the positions of the Scholars, as it relates to these aḥādīth and verses. As such, they have left the straight path to the extent that they gather and one of them reads something from the Qurʾān and he has a nice voice, a good tone and makes it melodious to the point that it resembles blameworthy musical singing. Then they say, ‘Come join us in remembering/mentioning Allāh.’ They then raise their voices and take turns in this ‘dhikr’, alternating amongst themselves. One group on one side, another on the other side, reciting with one sound resembling music. Then they claim that these are the recommended gatherings of dhikr. 

They have lied, because if this were the truth, the righteous predecessors were more deserving to have known this, understood it and acted upon it. If this is not the case, where in the Book and the Sunnah is there mention of gathering to make dhikr out loud in unison? Allāh states, 

ٱدْعُوا۟ رَبَّكُمْ تَضَرُّعًا وَخُفْيَةً إِنَّهُۥ لَا يُحِبُّ ٱلْمُعْتَدِينَ

‘Supplicate to your Lord in humility and in secret. He does not love the transgressors.’ [al-Aʿrāf 7:55].”

1 Al-Iʿtiṣām, (vol.2, pgs. 92-93).
2 In which they claim to remember Allāh by reciting incantations that have no validity from the Prophet (صلى الله عليه وسلم) or his Companions.