Musar על ישעיהו 66:23

And he who makes his heart as nothing but flesh — his prayer will be heard, as it is written: "All flesh will come to bow before Me, said the Lord" (Is. 66:23) (See Sotah 5a). And it is written: "O Thou that hearest prayer, unto Thee does all flesh come" (Ps. 65:3).