Scriptural   references for Hare Krishna maha mantra:-

One of these names is “Krishna” which means “He who is all-attractive,” another is “Rama” which means “He who is the reservoir of all pleasure,” and “Hare” indicates the Lord’s inconceivable energy.

All the grievous sins are removed for one who worships Lord Hari, the Lord of all lords, and chants the holy name, the Maha-mantra. (Padma Purana, 3.50.6)

One who chants the holy name of the Lord is immediately freed from the reactions of unlimited sins, even if he chants indirectly (to indicate something else), jokingly, for musical entertainment, or even neglectfully. This is accepted by all the learned scholars of the scriptures. (Srimad-Bhagavatam, 6.2.14)

My dear King, although Kali-yuga is an ocean of faults, there is still one good quality about this age: Simply by chanting the Hare Krsna maha-mantra, one can become free from material bondage and be promoted to the transcendental kingdom. (Srimad Bhagavatam – 12.3.51)