I don't have the exact quote nektarios but to paraphrase st Basil refered to the ancient greek philosophers as nectar from the flowers that we must gather and use in conjunction with the what we already have
The quote went along the lines of that we ought to emulate bees who take only that which is good from all the flowers and produce sweet and pure honey.
I would be very interested in those quotes whenever you get the chance.
I guess the first and most obvious is St. Paul in starting in Acts 17:22. If any Orthodox bishop were to speak in such a manner today, he would be condemned as an ecumenist, syncretists, new calendarist or whatever else (to be honest, I'm surprised certain EO sects haven't taken St. Paul out of the synaxarion...). To say that a God worshipped by Pagans is the Christian God is certainly a step further than saying the Abrahamic God worshipped by other monotheists is the same as the Christian God.
St. Justin Martyr:
"Those who lived in accordance with the Logos are Christians, even though they were called godless, such as, among the Greeks, Socrates and Heraclitus and others like them."
The Greeks speak of God as the Logos...for Logos signifies both speech and reason, inasmuch as he is both the voice and the wisdom of God. And of this Divine voice not even the philosophers were ignorant, since Zeno represents the Logos as arranger of the established order of things, and the framer of the universe: whom he calls Fate, and the necessity of things, and God, and the soul of Jupiter, in accordance with the custom, indeed, by which they are wont to regard Jupiter as God. But the words are no obstacle, since the sentiment is in agreement with the truth.
There are more quotes, but I'm kind of lazy. The basic outline of this idea is put forth very well in the book Christ the Eternal Tao
. The premise of the book is that if many fathers accepted ancient Greek philosophy as almost inspired (and the reality is that Christianity got the concept of the Logos from the Greeks, not the Hebrews), than ancient Daoism can be accorded the same respect. No mention is made of Islam - that is my own extension, if the pagan Greco-Roman philosophical tradition can be call worshipping the same God and the almost non-theistic ideas of Daoism, is Islam that much more of a stretch?
After the Incarnation, Death, Resurrection and Ascention of Christ, and after His command to the Apostles to go and 'make disciples of all nations', the knowledge of God is no longer for an exclusive group, but for the whole world. Islam came along, took a corruption of the Truth and perverted it further. Thus, even if we were to argue that the ancients worshipped God in their own right, I do not see how we can argue the same for Islam.
To that I'd argue that St. Paul still told the Athenians that their unkown God was the Christian God after the Christian revelation. The reality is also that in most of the Islamic world, the social and political conditions make the open knowledge and preaching of Christianity all but impossible. I'm not as familar with Arab and North African Islam but the typical central Asian Muslim lives in a state with a Soviet style near dictatorship and his only exposure to Christianity has been Russian chauvanism and colonialism - so is it really accurate to judge such a person as having heard the Christian Gospel and rejected it?