The verse quoted here
harer nāma harer nāma harer nāmaiva kevalam kalau nāsty eva nāsty eva nāsty eva gatir anyathā
In this Age of Kali there is no other means, no other means, no other means for self-realization than chanting the holy name, chanting the holy name, chanting the holy name of Lord Hari.
It belongs to Brhan-Naradiya Purana 38.126 as per this. Is Brhan-Naradiya same as Narada purana? But I could not find the verse there in the 38th chapter.
What is the exact source of the verse?