Shiva Purana
सप्तदशप्रवाहेण नवमासैर्गतायुषम् ॥ अष्टादशदिनान्यत्र कथितं साधकेश्वरि ॥ ६४ ॥
If for seventeen days he dies within nine months. O fond of devotees, eighteen days too are mentioned here.
english translation
saptadazapravAheNa navamAsairgatAyuSam ॥ aSTAdazadinAnyatra kathitaM sAdhakezvari ॥ 64 ॥
hk transliteration by Sanscript