प्र-उपाभ्यां युजेर् अयज्ञ-पात्रेषु

The verb युजिर् 'to join' is svaritet, and consequently by sutra 1.3.72 it is always atmanepadi, when the fruit of the action accrues to the agent. The present sutra declares when this verb may take the terminations of atmanepada, even when the fruit of the action does not accrue to the agent. After the verb युज् preceded by the prepositions प्र and उप the terminations are of the atmanepada, when not employed in reference to sacrificial vessels. As प्रयुङ्क्ते 'he joins or employs'; उपयुङ्क्ते 'he fits or uses.'

Why do we say \when not employed in reference to sacrificial vessels?\ Because there the terminations will be of the parasmaipada. As द्वन्द्वं न्यञ्चि पात्राणि प्रयुनक्ति.

Vartika:- It shall be rather stated that the root takes the terminations of the atmanepada when preceded by any preposition beginning or ending with a vowel. This is an important modification of the above rule. Thus उद्युङ्क्ते and नियुङ्क्ते. In fact, all upasargas, with the exception of सम्, निर्, and दुर्, either begin or end with a vowel, and therefore the Vartika amounts to the inclusion of all prepositions with the above exception.

With सम्, निर् and दुर्, however, the root will take parasmaipada terminations; as संयुनक्ति.,