Yochanan I 4:2-3

2 By this we have da’as of the Ruach Hakodesh of Hashem: every ruach which makes hoda’ah (confession) of Yehoshua, Rebbe, Melech HaMoshiach as having come in the basar is of Hashem,

3 And every ruach which does not make hoda’ah of Yehoshua is not of Hashem. And this is the ruach of the Anti-Moshiach, which you have heard that it is coming; and now it already is in the Olam Hazeh.