Midrash for Joshua 4:9

Thus it is to be found that there were three kinds of stones, one was that which Moses erected on this side of the Jordan, as it is said (Deut. 1, 5) And this side of the Jordan, in the land of Moab, began Moses to explain this law and it is said further, (Ib. 27, 8) And thou shalt write upon the stones all the words of Ba'er [to explain], and we infer through analogy applying the similar word Ba'er used in both places. Another kind of stone was that which Joshua set up in the Jordan, as it is said (Josh. 4, 9) Twelve stones also did Joshua set up in the midst of the Jordan; and the third are the stones which Joshua set up in Gilgal, as it is said (Ib., ib., 20) And those twelve stones, which they had taken out of the Jordan, did Joshua set up in Gilgal.