वारणार्थानामीप्सितः

Definition saṃjñā कारकसंज्ञाDefinition saṃjñā अपादानसंज्ञा

In case of verbs having the sense of 'preventing, the desired object from which one is prevented or warded off', is called Ablation or अपदान कारक.

Word by word (padaccheda)

Of वारण- अर्थानाम् ṣaṣṭhī · bahuvacanaTerm / subject ईप्सितः prathamā · ekavacana

Of Ṣaṣṭhī (6th case): "of X". In this kind of sūtra it marks a relation, not a substitution.
Term / subject Prathamā (1st case): the term being defined, or the subject of the statement.

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Full reading

वारण-अर्थानाम् ईप्सितः

Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.

Commentary

In case of verbs having the sense of 'preventing, the desired object from which one is prevented or warded off', is called Ablation or अपदान कारक।
The obstruction to one's natural inclination is called varana or prevention. As यवेभ्यो गां वारयति or निवर्तयति he wards off or withholds the cow from the barley.

Why do we say 'the object desired' is put in the ablative case' ? Observe गां वारयति क्षेत्रे he wards off the cow in the field.

Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.