Natyashastra
तृतीयं च चतुर्थं च गुरूणि पञ्चमं लघु । प्लुतान्तः षट्पितापुत्रो गुरुलाघवसंयुतः ॥ १९॥
The third and fourth syllables are long, the fifth is short, and it ends with a pluta syllable. This is the Ṣaṭpitāputraka, composed of a combination of long and short syllables.
english translation
tRtIyaM ca caturthaM ca gurUNi paJcamaM laghu । plutAntaH SaTpitAputro gurulAghavasaMyutaH ॥ 19॥
hk transliteration by Sanscript