ह्लादो निष्ठायाम्

Operational rule vidhi

The penultimate of the Causative of ह्लद् (ह्लादि) is shortened before the Participle affixes क्त and क्तवतु.

Word by word (padaccheda)

Target ह्लादः ṣaṣṭhī · ekavacanaRight context निष्ठायाम् saptamī · ekavacana

Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).
Right context Saptamī (7th case): "when X follows", the operation applies to what precedes (1.1.66 तस्मिन्निति निर्दिष्टे पूर्वस्य). Also a condition or domain ("in the sense of").

Dotted words are technical terms, dashed ones pratyāhāras (names for classes of sounds or affixes). Hover or tap one to see its card.

Full reading

ह्लादः निष्ठायाम्

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

Commentary

The penultimate of the Causative of ह्लद् (ह्लादि) is shortened before the Participle affixes क्त and क्तवतु।
Thus प्रह्लन्नः, प्रह्लन्नवान्, but प्रह्लादयति before non-nishtha. The rule applies also when क्तिन् follows as प्रह्लत्तिः ॥ This is done by splitting up the aphorism into two (1) ह्लादः (2) निष्ठायाम् ॥

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