Question: Where does it say that in the Holy Scriptures?
Answer: It is nowhere to be found. On the contrary. Let the Bible speak for itself.
First of all, it should be clarified where the number 144,000 comes from. This can be answered very simply: This number, 144,000, appears exactly twice in the HS, both times in the book of Revelation, in chapters 7 and 14, whereby chapter 14 refers back to chapter 7. We read there, in verses 4 to 8:
(Elberfelder Study Bible Edition)
We can quite clearly see that we are talking here about 144,000 sealed Jews. These Jews (or "Jewish Christians") form a remnant of this people who have accepted Christ and stand before the throne of God, as is written in context.
The Jehovah's Witnesses, however, explain this quite differently: they seriously claim that this is a pictorial discourse that speaks of "spiritual Jews". It is said that they cannot be natural Jews, because today no Jew knows any more to which of the tribes he belongs and therefore no classification can be made.
While it is true that no Jew today can say with certainty any more to which of the tribes he belongs, this is not an argument to the effect that the Bible's statement would be considered inadequate with regard to this. In order to believe in Jesus or be circumcised in his heart, as Paul calls it, a Jew need not be in the knowledge of his family tree. Paul completely rejects this (Epistle to the Romans, chapter 2, verses 28 and 29).
The HS names the 144,000 exactly as carnal Jews and nothing else. Anyone who claims otherwise here consciously remodels the statement of Scripture. What Scripture itself says about this (about remodeling) can be read quite simply. One reads in addition 5. book Moses (Deuteronomy), chapter 4, verse 2 as well as book of the revelation, chapter 22, the verses 18 to 19.
In a congress in 1935(?) of the JW the separation of the 144,000 - according to the teaching of the WTS, not the HS - from "the other sheep" from John's Gospel, chapter 10, verse 16 was made, whereby these two documents (Revelation and John's Gospel) are in no way connected. The "other sheep" of which Jesus speaks in this passage merely refer to persons in other places, but by no means to another "class" of Christians, as the WTS primarily claims. That this does not fit together can also be seen from the statement by Pauli, who speaks of "one faith, one baptism and one hope" (Ephesians letter, chapter 4, verses 4 and 5) and not of one faith, one baptism and two hopes, which would be the case, according to the WTS doctrine ("two hopes") ("two hopes"): A heavenly one (the 144,000) and an earthly one ("the great multitude").
With this two-class teaching, it prevents millions of her faithful followers from breaking bread and drinking wine during the Lord's Supper. But the commandment is unequivocal: Take of it, without any exception catalogue or note in this regard (Matthew's Gospel, chapter 26, verses 26 to 28 and John's Gospel, chapter 6, verses 53 to 59).
Question: Who might be interested in any people not obeying this commandment, which was even given directly by God's Son? And that they are cut off from Jesus, who is pure life, according to the texts mentioned here? An organization of God or a mouthpiece of God certainly not! If so, then it is more of an opponent of God. And who that is again, is also clear!
Very, very good arguments as to who may or may not celebrate the Lord's Supper where and when can be found in the little booklet "Das Abendmahl - Biblische Grundlagen für eine lebendige Gemeindepraxis" (The Lord's Supper - Biblical Foundations for a Living Church Practice), published by Forum Wiedenest, author: Ulrich Neuenhausen.