Buddha-carita, or Life of Buddha by Ven. Aśvaghoṣa

Buddha-carita, or Life of Buddha - 153
78. ‘The body-knower (the soul) which is unembodied, must be either
knowing or unknowing; if it is knowing, there must be some object to
be known, and if there is this object, it is not liberated.
79. ‘Or if the soul is declared to be unknowing, then of what use to
you is this imagined soul? Even without such a soul, the existence of
the absence of knowledge is notorious as, for instance, in a log of
wood or a wall.
80. ‘And since each successive abandonment is held to be still
accompanied by qualities, I maintain that the absolute attainment of
our end can only be found in the abandonment of everything.’
81. Thus did he remain unsatisfied after he had heard the doctrine of
Arāḍa; then having decided it to be incomplete, he turned away.
82. Seeking to know the true distinction, he went to the hermitage of
Udraka, but he gained no clear understanding from his treatment of
the soul.
83. For the sage Udraka, having learned the inherent imperfections of
the name and the thing named, took refuge in a theory beyond
Nihilism, which maintained a name and a non-name.
84. And since even a name and a non-name were substrata, however
subtil, he went even further still and found his restlessness set at rest
in the idea that there is no named and no un-named;