What is the difference between bid'ah (religious innovation) and maslahah mursalah (unrestricted public benefit)?

The Shaykh : Ibn Taymiyyah (may Allah have mercy on him) has a very important study in his book *Iqtida' al-Sirat al-Mustaqim Mukhalafat Ahl al-Jahim* regarding the distinction between bid'ah (religious innovation), which, as you know, is generally considered misguidance, as he (peace and blessings be upon him) said: , and maslahah mursalah (unrestricted public benefit). This is very similar in that there is a connection between the two and a very precise point of divergence. He says, among other things, that this discussion is lengthy: The newly occurring matter is either one whose cause for its existence existed in the time of the Messenger of Allah (peace and blessings be upon him), or it did not exist. If the cause existed and the Messenger of Allah (peace and blessings be upon him) did not legislate it, or did not establish that which is being introduced under the claim of maslahah mursalah (unrestricted public benefit), then this is attached to bid'ah (religious innovation) that is misguidance. However, if the cause did not exist in his time (peace and blessings be upon him) and then it appeared, he says: One looks to see if the motive for adopting this cause is the negligence of the Muslims in applying the rulings of the Shari'ah. If so, it is not permissible to adopt it, because in this case they are commanded to take the rulings of the Shari'ah, which suffices them from introducing something that was not in the time of the Messenger (peace and blessings be upon him), even under the claim of achieving a benefit. But if the motive for adopting the cause is not the negligence of the Muslims, then one looks to see if it leads to the realization of a Shari'ah benefit. If it does, this is the place of maslahah mursalah (unrestricted public benefit); otherwise, it is not.