A daughter sent at dusk
Vishrava is a sage, the son of Pulastya and grandson of Brahma himself. His penances are great, and his fire burns like a fourth flame added to the sacred three. When the rakshasa lord Sumali wishes to recover the power his kind has lost, he sends his daughter Kaikasi to seek sons from this twice-born ascetic — and he sends her at dusk, the fierce hour.
The Uttarakanda tells the meeting. Kaikasi stands before Vishrava as he performs the Agnihotra, hanging her head down toward his feet, drawing lines in the earth with her great toe. She is beautiful as the full moon. He asks who she is and why she has come. She answers that her father sent her, and that the sage may read the rest himself.
The warning at the fierce hour
Vishrava enters into contemplation and speaks the truth of what will come:
Inasmuch as thou hast come to me at this fierce hour, hearken, thou amiable one, as to the kind of offspring that thou shalt bring forth. Thou shalt, O thou of graceful hips, bring forth terrible and grim-visaged Rakshasas delighting in frightful friends, and of cruel deeds. — Ramayana, Uttarakanda, tr. M. N. Dutt
The hour is the cause. Because she came at dusk, the sons will be cruel. Vishrava does not refuse her, but he tells her what the timing has determined. Kaikasi objects: she did not come to him for such sons. It is not fitting, she says, that a follower of the Veda should give her offspring of terrific ways.
Vishrava relents in part. The last son, he says, will be different. Born later, after the fierce hour has passed, that child will be righteous and follow the sage’s own line. This is Vibhishana, who will one day leave Ravana’s side and join Rama in the war against his own brothers.
Four children and one outcome
Kaikasi bears four children to Vishrava: Ravana, Kumbhakarna, Shurpanakha, and Vibhishana. The first three fulfil the prophecy of the fierce hour. Ravana carries off Sita and brings war to Lanka; Kumbhakarna sleeps through half the epic and wakes only to die; Shurpanakha’s desire for Rama sets the abduction in motion. Vibhishana alone turns away and survives, his righteousness protecting him from the doom that takes his siblings.
The sage’s warning was exact. The hour mattered. What Sumali sent his daughter to obtain, he obtained — but the terms were set before any child was born, in a single sentence about the time of day.