for example the nickname of Imam Mahdi is Aba Saleh (the father of Saleh) or the nickname of Imam Ali is Abu Turab (the father of Turab) even though he did not have a child by the name of Turab.
[1] Ibn Nama Hilli, Muthirul-Ahzan, pg. 7; Majlisi, Biharul-Anwar, vol. 45, pg. 47.
