Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Councils of Ancyra, Gangra, Neocæsarea, Antioch and Laodicea, which Canons were Accepted and Received by the Ecumenical Synods.: Canon XII

Canon XII.

If any one be baptized when he is ill, forasmuch as his [profession of] faith was not voluntary, but of necessity [i.e. though fear of death] he cannot be promoted to the presbyterate, unless on account of his subsequent [display of] zeal and faith, and because of a lack of men.

Notes.

Ancient Epitome of Canon XII.

One baptized on account of sickness is not to be made presbyter, unless in reward for a contest which he afterwards sustains and on account of scarcity of men.

The word used in the Greek for “baptized” is “illuminated” (φωτισθῇ), a very common expression among the ancients.

Aristenus.

He that is baptised by reason of illness, and, therefore come to his illumination not freely but of necessity, shall not be admitted to the priesthood unless both these conditions concur, that there are few suitable men to be found and that he has endured a hard conflict after his baptism.

p. 85 With this interpretation agree also Zonaras and Balsamon, the latter expressly saying, “If one of these conditions is lacking, the canon must be observed.”  Not only has Isidore therefore missed the meaning by changing the copulative into the disjunctive conjunction (as Van Espen points out) but Beveridge has fallen into the same error, not indeed in the canon itself, but in translating the Ancient Epitome.

Zonaras explains that the reason for this prohibition was the well-known fact that in those ages baptism was put off so as the longer to be free from the restraints which baptism was considered to impose.  From this interpretation only Aubespine dissents, and Hefele points out how entirely without reason.

This canon is found in the Corpus Juris Canonici, Gratian’s Decretum., Pars. I., Dist. lvii., c. i.