It is said in the Chhaandogya Upanishac:- "The soul after being emancipated never comes back again into this world." CHHAANDOGYA 8:7, 1.
"Again it is written in the Vedaant Shaastras: "The Veda declares there is no coming back, no coming back declares the Veda."VEDANT SHAASTRA 4: 4, 33.
The Gita also says:- "That Supreme State from which it - the soul - never falls back (into this world) is mine."