Not long after the accession of Valens, Basil was ordained presbyter by Eusebius.  An earlier date has been suggested, but the year 364 is accepted as fitting in better with the words of Gregory  on the free speech conceded to heretics. And from the same Letter it may be concluded that the ordination of Basil, like that of Gregory himself, was not wholly voluntary, and that he was forced against his inclinations to accept duties when he hesitated as to his liking and fitness for them. It was about this time that he wrote his Books against Eunomius;  and it may possibly have been this work which specially commended him to Eusebius. However this may be, there is no doubt that he was soon actively engaged in the practical work of the diocese, and made himself very useful to Eusebius. But Basil's very vigour and value seem to have been the cause of some alienation between him and his bishop. His friend Gregory gives us no details, but it may be inferred from what he says that he thought Basil ill-used.  And allusions of Basil have been supposed to imply his own sense of discourtesy and neglect.  The position became serious. Bishops who had objected to the tumultuary nomination of Eusebius, and had with difficulty been induced to maintain the lawfulness of his consecration, were ready to consecrate Basil in his place. But Basil shewed at once his wisdom and his magnanimity. A division of the orthodox clergy of Cappadocia would be full of danger to the cause. He would accept no personal advancement to the damage of the Church. He retired with his friend Gregory to his Pontic monasteries,  and won the battle by flying from the field. Eusebius was left unmolested, and the character of Basil was higher than ever. 
 It will have been noted that I have accepted the authority of Philostorgius that he was already deacon. The argument employed by Tillemont against this statement is the fact of no distinct diaconate being mentioned by Gregory of Nazianzus. But the silence of Gregory does not conclusively outweigh the distinct eti taxin diakonou echon of Philostorgius; and a diaconate is supported by the mistaken statement of Socrates (H.E. iv. 26) that the deacon's orders were conferred by Meletius.
 Greg. Naz., Ep. viii.
 cf. Ep. xx.
 Greg. Naz., Orat. xliii. 28, Epp. xvi.-xvii.
 e.g. Hom. in Is. i. 57, alazoneia gar deine to medenos oiesthai chrezein.
 Gregory has no doubt that Eusebius was in the wrong, even ridiculously in the wrong, if such be the true interpretation of his curious phrase (Or. xliiii. 28), haptetai gar ou ton pollon monon, alla kai ton ariston, ho Momos. The monasteries to which Basil fled Gregory here (id. 29) calls phrontisteria, the word used by Aristophanes (Clouds, 94) of the house or school of Socrates, and apparently a comic parody on dikasterion. It might be rendered "reflectory." "Contemplatory" has been suggested. It is to be noted that Basil in the De Sp. Scto. (see p. 49, n.) appears to allude to the Acharnians. The friends probably read Aristophanes together at Athens.
 Greg. Naz., Or. xliii. Soz. vi. 15.
Reference address : https://www.elpenor.org/basil/life-works.asp?pg=14