नञः शुचीश्वरक्षेत्रज्ञकुशलनिपुणानाम्

Before a तद्धित affix having an indicatory ञ् , ण् or क् , the वृद्धि is always substituted for the first vowel of 1. शुचि 2. ईश्वर 3. क्षेत्रज्ञ 4. कुशल and 4. निपुण when preceded by the Negative particle, but this substitution is optional for the vowel of the Negative particles.
As अशौचम् or आशौचम्, अनैश्वर्यम् or आनैश्वर्यम्, अक्षैत्रज्ञ्यम् or आक्षैत्रज्ञ्यम्, अकौशलम् or आकौशलम्, अनैपुणम् or आनैपुणम् ॥ Some say the optional vriddhi of the negative particle is an aprapta-vibhasha, no other rule would have caused its vriddhi had this rule not existed. They argue that by 5.1.121, all affixes denoting भाव are prohibited after a Tatpurusha compound with the negative particle; therefore, the words शुचि &c, should be first developed by the addition of भाव-affixes, and then they should be compounded with the negative particle, which may be optionally vriddhied by this rule, which would apply to it, though it is not an anga, because the rule teaches vriddhi. Others controvert this opinion, and hold that other affixes causing vriddhi than भाव-affixes, also come after negative-Tatpurusha compounds, such as affixes denoting descendant &c: and भाव-affixes are added to Bahuvrihi negative compounds also, therefore, the force of the anuvritti of अङ्ग, which is understood up to the end of the Seventh Adhyaya 6.1.1, and a fortiori in this sutra also, should not be set aside as the above interpretation would do. Moreover the full Taddhita compounds अक्षेत्रज्ञ and अनीश्वर are read in the list of Brahmanadi words 5.1.124, and as such they take the भाव affix ष्यञ् which would have always caused the vriddhi of अ, but for this sutra which makes it optional. Therefore it is a prapta-vibhasha.