Shiva Purana

siva.sh/siva-purana/uma-samhita/25/59

नाडी यदा च वहति त्रयोदशदिनावधि ।। सम्वत्सरं भवेत्तस्य चतुर्मासाः प्रकीर्तिताः ।। ५९।।

sanskrit

And when the vein carries for thirteen days. It is said to be a year and four months.

english translation

nADI yadA ca vahati trayodazadinAvadhi || samvatsaraM bhavettasya caturmAsAH prakIrtitAH || 59||

hk transliteration by Sanscript