First Council of Nicaea, Canon IV

It is by all means proper that a bishop should be appointed by all the bishops in the province; but should this be difficult, either on account of urgent necessity or because of distance, three at least should meet together, and the suffrages of the absent [bishops] also being given and communicated in writing, then the ordination should take place.  But in every province the ratification of what is done should be left to the Metropolitan.

Translation: Henry R. Percival, The Seven Ecumenical Councils, NPNF II.14 (1900), via CCEL.