It is very common in Arabic that when the word Ibn
is used in the vocative case (Munādā), particularly when used at the time of
expressing affection and love, the appended noun (Mudaf-ilayh) can be declined
in the nominative case (Marfu‘), accusative (Mansūb) as well as the genitive (Majrūr)
case. All the three forms are used by the Arabs at such instances, as is
specified by the celebrated grammarian Zamakhsharī in his treatise on Arabic
Grammar (section on Munādā).