Adbhutasagara 48.57

48.57

jalamadhye'nāvṛṣṭi......iti|
viṣṇudharmottare|
śakracāpaṃ jale dṛṣṭvā gagane vā dvijottama|
avidyamānaṃ dharmajña tṛtīye mriyate dhruvam||

"In the middle of the water, a drought..." and so forth.
In the Viṣṇudharmottara:
"Having seen a rainbow in the water or in the sky, O best of the twice-born,
when none exists, O knower of dharma, he definitely dies on the third [month]."