Council of Ephesus
Council of Ephesus, Canon II
Selected letters, decrees and canons, including Cyril’s anathemas with reception notes; not the full proceedings
Canon II
If any provincial bishops were not present at the holy Synod and have joined or attempted to join the apostacy; or if, after subscribing the deposition of Nestorius, they went back into the assembly of apostates; these men, according to the decree of the holy Synod, are to be deposed from the priesthood and degraded from their rank.
Translation: Henry R. Percival, The Seven Ecumenical Councils, NPNF II.14 (1900), via CCEL.
Source: Council of Ephesus (CCEL)