So I’ll try to clarify what I meant.
I argued during the discussion that I know God exists. In response, it was claimed that it is impossible to know that God exists, and one can only believe in His existence.

Some clarification. I assume that in the next clarification you’ll write something like: Reuven said that he believes, and I told him that I know it’s more than believing. And so on.

I can offer the help of the Michi Bot:

Hello! Before we dive in: the answers here are given by a model that learns from the sources of Rabbi Michael Abraham and tries to reconstruct what he would answer; they do not necessarily reflect his actual position. For practical questions of Jewish law, one should consult a halakhic decisor. In addition, the Michi Bot is intended for the GPT-5 Thinking model—it’s worth making sure that this is the model you’re using.

The short answer: yes—according to Rabbi Michael Abraham’s line of thought, one can “know” that God exists in the ordinary epistemic sense (justified knowledge, though not mathematical certainty). In fact, for him “belief” in the cognitive sense = “knowledge.” (Rabbi Michael Abraham)

Why this is knowledge even without “conclusive proof”

Knowledge != certainty

Most human knowledge—from physics to history—is not 100% certain, and yet we still call it “knowledge.” So too regarding God’s existence: there are good reasons that establish a strong rational basis for belief, even without apodictic proof. (Rabbi Michael Abraham)

Cumulative evidence

The Rabbi gathers together types of arguments (in the Kantian classification tradition): ontological, cosmological, teleological, and more; the evidential perspective is cumulative and not “one arrow that knocks everything down.” In the book God Plays Dice, a chapter is devoted to “proofs of the existence of God,” and there is an appendix, “What Is a Proof,” that sharpens what exactly counts as proof in such contexts. On the site he emphasizes that the discussion of proofs is philosophical (not “Jewish thought” in the yeshiva sense), which marks a clear methodological standard. (Rabbi Michael Abraham)

Knowledge can be binding even without direct empiricism

Sometimes the argument that shows “I am compelled to think that there is a God” is sufficient—and from his perspective that too is valid as knowledge about the world, so long as I am not a radical skeptic. (Rabbi Michael Abraham)

“Belief” in the religious sense versus “knowledge” in the philosophical sense

It is important to distinguish between:

1.

Philosophical knowledge/belief: the rational conclusion that a supreme being exists.

1.

Religious belief: commitment to the worship of God, acceptance of revelation, and the like. The first does not require the second; one can be a deist (someone who believes in a philosophical God) without being a religious theist. (Rabbi Michael Abraham)

Practical conclusion

If by “knowledge” you mean absolute certainty—we have that for almost nothing. But if “knowledge” means an informed true position supported by good reasons, then one can certainly know that God exists, and not merely “believe” in the sense of a gamble or a feeling. For Rabbi Abraham, this is literally the same thing in the dictionary: belief (in the cognitive sense) = non-certain but rational knowledge. (Rabbi Michael Abraham)

Would you like me to spell out a particular type of argument (cosmological / teleological / ontological), or show how they are combined into a single “web of evidence”?

Sources actually used

“Belief or Knowledge” — on Rabbi Michael Abraham’s site (link: mikyab.net/responsa/belief-or-knowledge). (Rabbi Michael Abraham)

“Another Look at Proofs, Belief, and Religious Language (Column 513)” — a post on the site. (Rabbi Michael Abraham)

“Notebooks on Matters of Belief” — worksheets on the site (a survey of types of arguments). (Rabbi Michael Abraham)

“Jewish Thought / Proofs for the Existence of God” — an answer on the site (philosophical framing). (Rabbi Michael Abraham)

God Plays Dice — chapter “Proofs for the Existence of God”; Appendix A: “What Is a Proof”; the framework of the three kinds of proofs.

To get a deeper and more accurate picture, it is recommended to study the cited sources.

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If you want, I can also remove links / parentheses entirely, or replace question marks / colons / numbers according to stricter rules.