putras te bhavita bhadre
samvatsaram vratam idam
yady añjo dharayisyasi
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Kasyapa Muni said: My dear gentle wife, if you follow my instructions regarding this vow for at least one year, you will surely get a son who will be able to kill Indra. However, if you deviate from this vow of following the Vaisnava principles, you will get a son who will be favorable to Indra.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The word indra-ha refers to an asura who is always eager to kill Indra. An enemy of Indra is naturally a friend to the asuras, but the word indra-ha also refers to one who follows Indra or who is obedient to him. When one becomes a devotee of Indra, he is certainly a friend to the demigods. Thus the words indra-hadeva-bandhavah are equivocal, for they say, “Your son will kill Indra, but he will be very friendly to the demigods.” If a person actually became a friend of the demigods, he certainly would not be able to kill Indra.