Even the Eastern Orthodox Russian Patriarch, Krill holds to this belief:
“I know that there are Christians and Muslims, but each refers to the same God, the Creator, and in response to this we have the real God’s help.” (Source: On the day of the Resurrection of Christ, 16 April 2017)
The Eastern Orthodox saint, Gregory Palamas, who is a pillar of the Eastern Orthodox faith, believed Muslims and Christians worship the same God. When Palamas was captured by the Muslims he had a dialogue with them and said:
“As I was sitting there I asked whether anyone could speak both languages that I needed. There was somebody, whom I asked to say to the Turks [Muslims] on my behalf that what they had performed outside there I thought it was good, "for you addressed yourselves to God - to whom else? - for the deceased one. I wanted, however, to know what was that you exclaimed to God?" Tasimanes using the same interpreter said that he would explain: "We asked for forgiveness from God for the deceased, for his own sins committed in his soul." (Source: Saint Gregory Palamas, Littera & Dialexis Patrologia Migne –PG, CL, COL. DCCCVIII)
🔸 For Radical Traditionalists
As I’ve demonstrated earlier from the scriptures we see that the biblical writers clearly believed that Non-Christians who acknowledge a Creator worships the same God as Christians but in a false way. This isn’t a Vatican 2 invention and I’ll prove this further.
St. Pope Pius X taught Muslims and Christians worship the same God:
“Q. Who are infidels?
A. Infidels are those who have not been baptized and do not believe in Jesus Christ, because they either believe in and worship false gods as idolaters do, or though admitting one true God, they do not believe in the Messiah, neither as already come in the Person of Jesus Christ, nor as to come; for instance, Mohammedans and the like.”
(Catechism of Pope St. Pius X)
St. Robert Bellarmine (interpreting Jeremiah 31:33):
“But if someone contends that these last words too are to be understood of the present time, one can reply that here the Prophet is not speaking of the hidden mysteries of the Scriptures but of knowledge of the one God. For since in the time of the Old Testament not only did the Gentiles adore false gods but also very frequently the people of God turned to idols and strange gods, Jeremiah predicted the future, that in the time of the New Testament all men would know the one God, which we certainly see now to have been fulfilled. For the Gentiles have been converted to the faith, and also the Jews themselves and the Turks, although they are impious, yet worship the one God.”
Pope St. Gregory VII (His letter of 1076 to Al-Nasir, the Muslim Ruler of Bijaya):
“Almighty God, who wishes that all should be saved and none lost, approves nothing in so much as that after loving Him one should love his fellow man, and that one should not do to others, what one does not want done to oneself. You and we owe this charity to ourselves especially because we believe in and confess one God, admittedly, in a different way, and daily praise and venerate him, the creator of the world and ruler of this world.”
St. Justin Martyr believed Christians and Jews worship the same God:
"There will be no other God, O Trypho, nor was there from eternity any other existing, but He who made and disposed all this universe. Nor do we think that there is one God for us, another for you, but that He alone is God who led your fathers out from Egypt... Nor have we trusted in any other (for there is no other), but in Him in whom you have also trusted, the God of Abraham, and of Isaac, and of Jacob." (Dialogue with Trypho, ch. 11)
