Valmiki Ramayana Aranya Kanda Sarga 34 Shloka 18
Original Shlokaयस्य सीता भवेद्भार्या यं च हृष्टा परिष्वजेत्। अतिजीवेत्स सर्वेषु लोकेष्वपि पुरन्दरात्।।3.34.18।।
1 source checked for this shloka
यस्य whose, सीता Sita, भार्या as wife, भवेत् shall be, हृष्टा happily, यम् whom ever, परिष्वजेत् she may embrace, सः he, सर्वेषु in all, लोकेषु in the worlds, पुरन्दरात् अपि more than Indra, the breaker of fortress, अतिजीवेत् may wish to live long.
Whosoever gets Sita as his wife, whoever she embraces happily will wish to live longer than Indra, the breaker of fortresses in this world.