Second source:

This relates to the outer world. Observation and experience indicate the spirit's eternity. The individual spirit's permanence, which has been established in the afterlife, confirms the soul's perpetuation after death. It has been established logically that any essential aspect observed in an individual is common to the whole species, for qualities originating in the essence are shared by all individuals. Each soul's permanent existence after the body's death, as based on observation and countless experiences in dreams and other kinds of communication, is as certain as the existence of a continent that we have never visited. They have a relationship with us, for our prayers reach them and we receive their blessing in return. Moreover, it can be perceived that an essential aspect of each person exists after physical death: his or her spirit.

As the spirit is a simple unitary entity, it is not subject to disintegration or decomposition like composite material things. Life ensures a form of unity within multiplicity and causes a sort of permanence. In other words, unity and permanence are essential to the spirit, from which they spread to multiplicity.

The spirit's mortality would be due either to its decomposition and disintegration or its annihilation. The first option is impossible, for the spirit has a simple unitary essence. The second option also is impossible, for it is contrary to the Absolutely All-Generous One's infinite Mercy. Moreover, His boundless Munificence would not allow the human spirit to be deprived of the blessing of existence that He has bestowed on it, for it ardently desires and is worthy of this blessing.