Тосефта к Бамидбар 20:2

As long as Miriam was alive, there was a well that sustained Israel. Once Miriam died, what does it say, but (Num. 20:1-2), "Miriam died there ... And there was no water for the community," [meaning] that the well had disappeared. As long as Aaron was alive, the column of cloud guided Israel. Once Aaron died, what does it say, but (Num. 21:1), "And the Canaanite, the king of Arad, who ruled the Negev, heard [that Israel was coming]." That same evildoer raised an army and came to wage war with Israel. He said, "Where has their advance guard (התייר) gone, the one who was subduing the land for them?"