On the Councils
c. 359
De Synodis
Hilary’s survey of creeds and councils between Nicaea and the later settlements, including “like in substance” language. English in Nicene and Post-Nicene Fathers, Series II.
Translated by E.W. Watson, L. Pullan, et al.
English translation in Nicene and Post-Nicene Fathers, Second Series, Vol. IX (eds. Philip Schaff and Henry Wace; New York: Christian Literature Publishing Co., 1899). Public domain. Digital text via New Advent Church Fathers.