Is it obligatory to raise the forefinger in prayer when saying "Ashhadu an la ilaha illa Allah" (I bear witness that there is no god but Allah) and lower it when saying "Muhammadun Rasul Allah" (Muhammad is the Messenger of Allah), so as not to equate the Creator with the created, and is there any evidence for this?

Raising the index finger during the Tashahhud is recommended, not obligatory. The jurists' opinions regarding the beginning and end of its raising have been previously explained. As for what was mentioned about raising it when Allah Almighty is mentioned and lowering it when the Prophet, peace be upon him, is mentioned, as an indication of the difference between the Creator and the created, this has no basis.