Dear prabhuji,
Please accept my humble obeisances.
All Glories to Srila Prabhupada and Sri Guru Gauranga
I found some similar, not exact quotations:
1: Quoted from Srila Prabhupada by HH Danvir Gosvami Maharaj (The Hare Krsna Mahamantra is always succeeded by the arati):
Prabhupada’s general instructions on which songs and tunes to sing
He then went on to specifically describe how kirtana should be done.
A. For mangala aratika: the samsara-dava prayer, then Sri Krsna Caitanya (panca tattva
maha mantra), then Hare Krsna mahamantra, nothing else.
B. For the guru-puja: the "guru-prayer" (that's what he called it) Sri Krsna Caitanya
(panca tattva maha mantra), then Hare Krsna mahamantra, nothing else.
C. For evening aratika: the gaura aratika song, Sri Krsna Caitanya (panca tattva maha
mantra), and Hare Krsna mahamantra, nothing else....
HH Danavir Goswami Maharaj, On chanting.
Reference: Kirtan Standards Book pg. 88
2: Room Conversation:
Prabhupāda: No. This is... In this age temple worship is not recommended.
Haṁsadūta: It's not recommended. But Deity worship is temple worship?
Prabhupāda: It is Deity worship. Because nobody can actually very nicely perform. This age is not suitable. You see? Temple worship, the regulation, the engagement—at least four, five men must always be engaged, always, twenty-four hours.
Haṁsadūta: In the temple worship. In the temple.
Prabhupāda: Yes. We haven't got sufficient men, neither we can arrange such a way. Besides that, your previous culture, everything is completely different. So in this age Caitanya Mahāprabhu has..., this saṅkīrtana, Hare Kṛṣṇa, harer nāma harer nāma harer nāma [Cc. Ādi 17.21].... This is all round. But at the same time, if you can perform as far as possible, that's nice, Deity worship. In this age Deity worship is secondary. Saṅkīrtana is primary.
Reference: Room Conversation 1, 24th April 1969, Boston
3: Srila Guru Maharaja's quotation for half of the arati to consist of the Hare Krsna Mahamantra:
...In ISKCON, only two simple akharas are common: the lines gaurangera arotika sobha jaga jana mana lobha and sankha baje ghanta baje madhura madhura baje, sung in the Gauraarati kirtana. Some ISKCON devotees, especially from Bengal, sing äkharas for every line of the Gaura-arati song. However, as Srila Prabhupada wanted that chanting of Hare Krsna take up at least half of the arati kirtana, and as he did not like new innovations, it is suggested that we stick to the form approved by Srila Prabhupada.
Srila Bhakti Vikasa Swami Guru Maharaja, Reference: Kirtan Standards Book pg. 43-44
4:
Although Srila Prabhupada himself taught us many other mantras, he always stressed the chanting of the Hare Krishna maha mantra. He said that at least half of the arati kirtana should consist of chanting of the Hare Krishna maha mantra. For example, in a temple where mangala-arati only lasts for 20 minutes, devotees should only sing each of the Gurvastakam once, in order to leave ten minutes for chanting Hare Krsna.
Ref: Srila Bhakti Vikasa Swami Guru Maharaja, Kirtan Standards Book pg. 146
Your servant,
Anvay