सम्पर्युपेभ्यः करोतौ भूषणे

Operational rule vidhi

The augment सुट् is placed before क when सम् , परि , and उप are followed by the verb कृ and the sense is that of ornamenting.

Word by word (padaccheda)

Left context सम्- परि- उपेभ्यः pañcamī · bahuvacanaRight context करोतौ saptamī · ekavacanaRight context भूषणे saptamī · ekavacana

Left context Pañcamī (5th case): "after X", the operation applies to what follows (1.1.67 तस्मादित्युत्तरस्य). Also used for limits and sources.
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").

Full reading

सम्-परि-उपेभ्यः करोतौ भूषणे

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

Commentary

The augment सुट् is placed before क when सम् , परि , and उप are followed by the verb कृ and the sense is that of ornamenting.
Thus संस्कर्ता, संस्कर्तुम्, संस्कर्तव्यम् ॥ The म् of सम् is changed to anusvara by 8.3.5. So also परिष्कर्ता परिष्कर्तुं परिष्कर्तव्यम् ॥ The स is changed to ष by 8.3.70. So also with उप, as उपष्कर्ता, उपष्कर्तुम् उपष्कर्तव्यम् ॥ Why do we say 'when meaning to ornament'? Observe उपकरोति ॥ Sometimes सुट् comes after सम् even when the sense is not that of ornamenting : thus संष्कृतमन्नम् ॥

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