There are, of course, many references in scripture and in early Christian writings to the relationship of bishops and deacons. The first letter to Timothy, for example, links the qualifications of the two.
The link between bishops and deacons is a profound one, and even when the Second Vatican Council took its own steps to renew a permanent diaconate in the Latin church, its discussions on the diaconate took place right in the middle of the discussions on the nature and role of bishops. In all of the literature since the Council, this relationship has been stressed.
Of all the ancient references, one of my favorites comes from Syria in the early 3rd Century, the Didascalia Apostolorum. This text offers practical directions for early church life in the area. Look at what it has to say about bishops and deacons:
Let the bishops and the deacons, then, be of one mind, and shepherd the
people diligently with one accord. For you ought both to be one body, father and
son, for you are in the likeness of the Lordship. . . . Let the deacon be the
hearing of the bishop, and his mouth and his heart and his soul; for when you
are both of one mind, through your agreement there will be peace in the Church.
. . . And be you both [bishop and deacon] of one counsel and of one purpose, and
one soul dwelling in two bodies.
Most deacons today would say that their own relationship with their bishops is not quite at this level yet! But it certainly gives a wonderful vision of how ordained ministry might be lived out in service of others. We often read and hear about the sacramental relationship that exists between presbyters (priests) and bishops, but we don't hear nearly enough about the analogous sacramental relationship that should likewise exist between bishops and deacons.