श्वीदितो निष्ठायाम्

Operational rule vidhi

The participial affixes त and तथत् (क्त and क्तवतु) do not get the इट् augment after श्वि and after the root which has an indicatory ई.

Word by word (padaccheda)

Target श्वीदितः 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").

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Full reading

श्वीदितः निष्ठायाम्

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

Commentary

The participial affixes त and तवत् (क्त and क्तवतु) do not get the इट् augment after श्वि and after the root which has an indicatory ई।
As शूनः, शूनवान; ओलेजी (VI.I0), - लग्न, लग्नवान्; ओविजी (VI.9), औद्विग्नः, उद्विग्नवान् ॥ The त is changed to न because of the indicatory ओ 8.2.45. So also दीपी (IV. 42), दीप्तः, दीप्तवान् ॥ In the Dhatupatha, डीङ् (IV. 27), is classed among ओदित् roots, and it indicates that the Nishtha is anit after it : and ओ is for न-change 8.2.45 as, उड्डीनः, उड्डीनवान् ॥ The word निष्ठायाम् governs the following sutras upto 7.2.35.

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