Karsnajini is a sage cited in Brahma Sutra on karma and conduct. He is referred to in Brahmasutra (III.1.9) of Badarayana and is represented there as holding the view that the departed souls after residing in heaven come back to earth with their residual acts (karma). This view accords with that of Shankara too.
The question that is raised in this aphorism of Brahmasutra (III-1.9), whether the departed souls, after experiencing in heaven the fruits of their actions during their lives on earth, come back with any residual action or without any such residue.
The prima facie view is that they descend to the Earth without any residue, as the scripture (Chandogya Upanishad, V-10.5; Brihadaranyaka Upanishad IV-4-6) declares that the souls reside in heaven till their karma is exhausted. The same texts also states that souls when they return are born as human beings or animals according to their good or bad conduct.
Some ancient sages were of the view that even though all the karma is exhausted by one’s stay in heaven, rebirth on earth is brought about by residual action. They thus make a distinction between actions and conduct.
Sage Karsnajini is quoted as rebutting this view. He says that the word accarana (conduct) used in the text should be construed as implying only moral actions (karma) and not conduct. Thus, acarana brings about only corresponding nuances in one’s karma, which directly determines destiny. So karma is the main cause of birth. Conduct is only a contributory factor. Sage Karsnajini concludes that, therefore, souls return to the earth after their stay in heave with their residual karma, not after exhausting such residue.