Is it true that before Sheikh Muhammad ibn Abd al-Wahhab, the four Imams would lead people in prayer, each according to his own madhhab, in the mosque? And why did that happen?

The multiplicity of congregations in the Grand Mosque (Masjid al-Haram (definition)) in the past was an innovation (bid'ah) that emerged in the sixth Hijri century. A specific station (maqam) for prayer was allocated to each jurisprudential school of thought, which led to the dispersion of worshippers and the intertwining of the imams' voices, especially during the Maghrib prayer. Scholars denounced this innovation due to its role in dividing Muslims and making them appear as if they belonged to various religions. This innovation persisted for nearly nine centuries until King Abdul Aziz Al Saud abolished it and unified the congregation behind a single imam. Scholars have affirmed that the spread of innovations and the silence of some scholars regarding them does not imply their permissibility or validity.