Islam and dating
This article is about the Hijri calendar based on lunar observation.For the solar calendar whose first year is fixed to the Hijra, see Solar Hijri calendar.
He also says that, in terms of the fixed calendar that was not introduced until 10 AH (632 AD/CE), the first intercalation was, for example, of a month between Dhu al-Hijjah and Muharram, the second of a month between Muharram and Safar, the third of a month between Safar and Rabi'I, and so on.
Some sources say that the Arabs followed the Jewish practice and intercalated seven months over nineteen years, or else that they intercalated nine months over 24 years; there is, however, no consensus among scholars on this issue.
Postponement (Nasī’) of one ritual in a particular circumstance does not imply alteration of the sequence of months, and scholars agree that this did not happen.
This is corroborated by an early Sabaic inscription, where a religious ritual was "postponed" (ns'’w) due to war.
According to the context of this inscription, the verb ns'’ has nothing to do with intercalation, but only with moving religious events within the calendar itself.