Uttering the words of Kufr while joking

Uttering the words of Kufr even if it is done while joking, renders a person Kaafir. One must be very careful. One must not utter statements, which contains Kufr, even while joking or teasing. Kufr is so serious that the Shar’iah does not tolerate it, even jokingly.

[English version of "Prononce banne parole de kufr dans badinage" – Al Jamiat – Vol.2 No.12]