Agnipurana 190.6

190.6

śrāvaṇādiṣu cārabhya kārttikānteṣu pāraṇaṃ /
saptajanmasu vaikalyaṃ vratānāṃ saphalaṃ kṛte //

and the concluding fast-breaking begins in the months starting with Śrāvaṇa and ending with Kārttika. / When it is performed, deficiency of vows across seven lifetimes becomes fruitful;