Though optional, Muhammad retained this pre-Islamic practice too.

Since Zaynab was the wife of Muhammad's adopted son, pre-Islamic practices frowned upon such her marriage with the prophet.

Some historians also linked the pre-Islamic practice of Nasi' to intercalation.

Syncretism is not unusual, where pre-Islamic practices and beliefs persist among Muslim communities.

Despite Muhammed's wishes, a cult of saints developed within Islam at an early date, following deeply ingrained pre-Islamic practices in the Middle East.

Soon after the Conquest of Mecca, Muhammad began to despatch expeditions on errands aiming at eliminating the last symbols reminiscent of pre-Islamic practices.

Thus several tribes acted in accordance to this pre-Islamic practice and refused to pay Zakat.

"How tragic it is that the pre-Islamic practice of female infanticide still haunts a world we regard as modern and civilized," she said.

Riba, he writes, was a pre-Islamic practice in which a "borrower saw his debt double following a default and redouble if he defaulted again."

Adat, as customary law is called in Indonesia, includes indigenous, pre-Islamic religious practices and social traditions in local custom.