The source for the requirement of minyan is recorded in the Talmud. The word minyan itself comes from the Hebrew root manehמנה meaning to count or to number. The word is related to the Aramaic word mene, numbered, appearing in Daniel 5:25.
"Speak to all the congregation of the children of Israel, and say to them: You shall be holy" (Leviticus 19:2)
is also used in another verse:
"How long shall I bear with this evil congregation which murmur against me?" (Numbers 14:27)
Since the term "congregation" in the later verse refers to the ten spies, so too in the former verse: "You shall be holy" refers to a "congregation" of ten.
The second source is based on the term "children of Israel" which appears in the following two verses:
"And I shall be sanctified in the midst of the children of Israel" (Leviticus 22:32)
" And the children of Israel came to buy among those that came" (Genesis 42:5)
Just as the "children of Israel" in the later verse refers to the ten sons of Jacob who descended to Egypt to obtain food during the famine, so too the former verse refers to sanctification among the “children of Israel” in the presence of ten.