Exodus 20:25
If you make an altar of stone for me, do not build it out of cut stones. This is because when you use a chisel on stones, you make them unfit for my use.
Deuteronomy 27:5-6
Build an altar there to Jehovah your God. Build the altar of stones. Do not use an iron tool on them.
Joshua 8:31
As Moses the servant of the Lord commanded the children of Israel, as it is written in the book of the Law of Moses, an altar of whole stones that have not been cut by any iron tool. They offered offerings to Jehovah, and sacrificed peace offerings.
Treasury of Scripture Knowledge
Summary
And if thou wilt make me an altar of stone, thou shalt not build it of hewn stone: for if thou lift up thy tool upon it, thou hast polluted it.
General references
Bible References
And
Deuteronomy 27:5
Build an altar there to Jehovah your God. Build the altar of stones. Do not use an iron tool on them.
Joshua 8:31
As Moses the servant of the Lord commanded the children of Israel, as it is written in the book of the Law of Moses, an altar of whole stones that have not been cut by any iron tool. They offered offerings to Jehovah, and sacrificed peace offerings.
General references
Leviticus 16:33
and perform the ritual to purify the Most Holy Place, the rest of the Tent of Jehovah's presence, the altar, the priests, and all the people of the community.