Yalkut Shimoni on Nach 15:8

"And they ate of the produce of the land on the day after the Passover" (Joshua 5:11). They asked Rav Kahana: The omer that Israel offered when they entered the land, from where did they bring it? If you say it came from grain in a gentile's possession, the Merciful One said "your harvest" (Leviticus 23:10), and not the harvest of a gentile. And from where do we know that they offered it at all? Perhaps they did not offer it? Do not let this enter your mind, for it is written, "And they ate of the produce of the land on the day after the Passover" (Joshua 5:11). "On the day after the Passover" they ate; beforehand they did not eat, because they offered the omer and only then ate. From where did they bring it? He said to him: from anything that had not yet reached a third of its growth in a gentile's possession. But perhaps such grain had entered the land yet they had no clear reckoning of it? Rather, they did have a reckoning; here too they had a reckoning. But perhaps it had not entered the land at all? Rather, they had a reckoning; here too they had a reckoning. But perhaps it had not entered at all, yet where grain had entered as a quarter or a sixth of its growth, between a third and less than a third they had no clear reckoning. Do not let this enter your mind, for it is written, "And the people came up out of the Jordan on the tenth of the month" (Joshua 4:19); and if it should enter your mind that it had not entered at all, could it have ripened in five days? Rather, granting that it entered at a quarter or a sixth, could it have ripened in five days? Rather, what is there for you to say? It is written of it, "a land of beauty" (Daniel 11:16); here too it is written of it, "a land of beauty."