Is it permissible to specify a certain dhikr (remembrance of God) with a number or a particular place without explicit textual evidence, and to act upon supplications and adhkar recommended by righteous predecessors based on their personal experiences, considering that some early scholars like Ibn Taymiyyah and Ibn al-Qayyim specified certain adhkar with particular numbers and times based on their experiences?

It is legislated to increase remembrance (dhikr) and supplication (du'a) in general. However, it is forbidden to specify certain remembrances or supplications with a particular number, time, place, or manner without a valid legal proof, and to persist in them as if they were a regular Sunnah.

The prophetic remembrances are the best to seek out, and no one has the right to legislate for people a type of remembrance that is not legislated and make it a regular act of worship. Sheikh al-Islam Ibn Taymiyyah differentiates between this and what a person might occasionally supplicate for themselves without making it a Sunnah for people.

Therefore, there is no harm in increasing the recitation of Al-Fatiha or verses of tranquility, or using proven supplications in ruqyah and medicine, provided that one does not persist in them as a regular Sunnah with a specific number or manner. Rather, this should be for the general benefit derived from the Quran, supplication, and seeking healing.

As for what has been transmitted from Sheikh al-Islam Ibn Taymiyyah regarding the persistence in the remembrance of "Ya Hayyu Ya Qayyum La ilaha illa Anta" forty times between the Sunnah prayer of Fajr and the Fajr obligatory prayer to achieve "the life of the heart," this restriction to a specific number and time lacks a specific proof from the Prophet's Sunnah. Sheikh al-Islam relied in this on the "experiences of wayfarers" or what was narrated from some righteous individuals, which are sayings that are not to be taken as binding legal rulings. Rather, they may sometimes be taken as a source of solace without adhering to them as an established Sunnah.

When a legal proof comes with a general command, such as the remembrance of Allah and supplication, it remains general. It is not permissible to restrict it with a specific manner, time, or place except with a legal proof. If this is done without proof, it becomes an innovated bid'ah.