Agniveshyagrihyasutra 2.5.11.4

2.5.11.4

saṃvatsare saṃvatsare ṣaṭsu ṣaṭsu māseṣu yadāmāvāsyāṃ śuṣyo bhavati yadā vṛṣṭerudaghātaṃ vindedatha bhūtabaliṃ dadyāt \

Year after year, every six months, when it is dry on the new-moon day, or when he observes an obstruction to rain, then he should offer the offering to beings.