innumerable sects became the cause of the shaking of the foundations of Islam.

The Holy Law (Sharí`ah) of the Messenger of God [Mohammed] may be likened to an ocean from which innumerable gulfs branch out. And this is the cause of the weakness of the Sharí`ah of God among the peoples. Until now no-one, not kings nor subjects nor the indigent have understood the reason for this, nor have they appreciated how to regain that power that has vanished and the learning that has fallen away. Thus one gulf is Shí`a, one gulf is Sunni, one Shaykhi, another Shah Ni`matulláhí, one Naqshbandi, another Malámatí, one Jalálí, another Rifá`í, and yet another Khárábátí. Thus are multiplied the innumerable pathways to hell. Thus do the stones weep and the Pen of the All-High laments. Seest thou what has befallen a Sharí`ah whose light illumined the world and whose fire, that is to say the fire of its love, was the guide of its peoples. Well is it with those who ponder upon these matters and investigate them and are fair in their judgement. Thus did this difference in rituals become the cause of the shaking of the foundations of the Cause of God [Islam].

(Lawh-i Ittihád, The Tablet of Unity, Bahá’u’lláh - provisional translation by Moojan Momen)

https://bahai-library.com/pdf/m/michot_tablets_bahaullah_3.pdf