Vaishnava Dharmashastra 49.10

49.10

tasyāṃ dānopavāsādyam akṣayaṃ parikīrtitam
tathaiva dvādaśī śuklā yā syāc chravaṇasaṃyutā //

Gifts, fasts, and the like are declared to be imperishable on that day. The same is the case if a conjunction with the asterism. Sravanâ falls on the twelfth day of the bright half (of any month).