What is the ruling on jesting by attributing oneself to other than one's father, and does the burden of the spread of such jesting fall upon its perpetrator?

It appears that what was mentioned falls under the category of insinuation aimed at denying the lineage of the Arab grandfather, which is forbidden and requires repentance. It may also fall under the category of slander (Qadhf), which is among the major sins. However, since the questioner does not intend to defame, no legal punishment (Hadd) applies to him. Nevertheless, he must refrain from such talk, even if it is in jest. It is forbidden for others to call him by this lineage, and whoever intends to deny the Arab lineage is considered a slanderer. Imam Al-Shafi'i stated that if someone tells an Arab man, "O Nabati," and intends to deny his lineage, then the Hadd punishment is imposed on him. Therefore, the questioner and others must refrain from such talk and repent to Allah.