Isaias 3 was a bishop and an iconophile, acquainted with Theodore the Stoudite (Theodoros 15), who mentions him in two of his letters. He delivered greetings to Theodoros 15 from Abolios 1 and Ioannes 335 (παρὰ Ἠσαΐου τοῦ θεοφιλεστάτου ἐπισκόπου καὶ πνευματικοῦ πατρὸς: p. 175, lines 2-3): Theod. Stud., Ep. 63, pp. 175-176 (dateable between 821 and 826, since Leo V (Leo 15) is dead). Isaias 3 and the unnamed hegoumenos of Medikion (possibly Niketas 43) obtained from the exiled empress Theodosia 1 a confession of faith accepting the veneration of icons; they conveyed it to Theodoros 15, who then wrote to the empress: Theod. Stud., Ep. 538, pp. 811-813 (Theodoros 15 received it παρά τε τοῦ θεοφιλεστάτου ἐπισκόπου Ἠσαΐου, p. 811, lines 2-3 - and from the hegoumenos of Medikion - ὁσίων πατέρων ἡμῶν, p. 811, line 4; they were ἀξιοπίστων προσώπων, p. 811, line 2) (the letter is dateable between 821 and 824, if the hegoumenos was Niketas 43, who died in April 824).

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