Prohibition of intercalation

Nasiʾ, Nasii, or Nasie (Arabic: النسيء‎‎, al-Nasīʾ, "postponement") was an aspect of the calendar of pre-Islamic Arabia, mentioned in the Quran in the context of the "four forbidden months". In pre-Islamic Arabia, the decision of "postponement" had been administered by the Banu Kinanah, by a man known as the al-Qalammas (pl. qalāmisa). Different interpretations of its meaning have been proposed.

Some scholars maintain that the pre-Islamic calendar used in Central Arabia was a purely lunar calendar similar to the modern Islamic calendar. According to this view, nasīʾ is related to the pagan practices of the Meccan Arabs, where they would alter the distribution of the forbidden months within a given year without implying a calendar manipulation. This interpretation is supported by Arab historians and lexicographers, like Ibn Hisham, Ibn Manzur, and the corpus of tafsir. Thus the Encyclopaedia of Islam concludes, "The Arabic system of [Nasīʾ] can only have been intended to move the Hajj and the fairs associated with it in the vicinity of Mecca to a suitable season of the year. It was not intended to establish a fixed calendar to be generally observed."

This interpretation is also corroborated by an early Sabaean language inscription, where a religious ritual was "postponed" (ns'ʾw) due to war. According to the context of this inscription, the verb ns'ʾ has nothing to do with intercalation, but only with moving religious events within the calendar itself. The similarity between the religious concept of this ancient inscription and the Qur'an suggests that non-calendaring postponement is also the Qur'anic meaning of Nasīʾ.

Others concur that the pre-Islamic calendar was originally a lunar calendar, but suggest that about 200 years before the Hijra it was transformed into a lunisolar calendar containing an intercalary month added from time to time to keep the pilgrimage within the season of the year when merchandise was most abundant. This interpretation was first proposed by the medieval Muslim astrologer and astronomer Abu Ma'shar al-Balkhi, and later by al-Biruni,al-Mas'udi, and some Western scholars. This view was also held by the Quran scholar and translator Abdullah Yusuf Ali.

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