Pāṇini sūtras

ṣ is substituted for the s of stut, stoma and soma when preceded by agni in a compound.

German In stut, stoma und soma nach agni. (82)

1. agneḥअग्नेः

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   aअ	agniअग्नि	agneḥअग्नेः	agni [word]	agnअग्न् + plus eḥएः

2. stut+stoma+somāḥस्तुत्+स्तोम+सोमाः

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   sस्	stutस्तुत्	stutस्तुत्	stut [word]	stutस्तुत्
   sस्	stomaस्तोम	stomaस्तोम	stoma [word]	stomस्तोम् + plus aअ
   sस्	somaसोम	somāḥसोमाः	soma [word]	somसोम् + plus āMआM

Anuvṛtti

1. a+pada+antasyaअ+पद+अन्तस्य 8·3·55

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   aअ	aअ	aअ	not	aअ
   pप्	padaपद	padaपद	word	padपद् + plus aअ
   aअ	antaअन्त	antasyaअन्तस्य	last syllable	antअन्त् + plus asyaअस्य

2. i+ṇ+koḥइ+ण्+कोः 8·3·57

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   iइ	iइ	iइ	ikāraइकार	iइ
   ṇण्	ṇण्	ṇण्	NaNअ	ṇण्
   kक्	kuकु	koḥकोः	guttural	kक् + plus oḥओः

3. samāseसमासे 8·3·80

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   sस्	samāsaसमास	samāseसमासे	Sanskrit compound	samāsसमास् + plus eए

4. saḥसः 8·3·56

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   sस्	sस्	saḥसः	sakāraसकार	sस् + plus aḥअः