The pre-Islamic Arabs had 354 days in their calendar rather than the 365 days of the solar calendar. To make up this difference, leap months were added once every three years. But this practice was discontinued in the year 629, and the Qur'an even forbids adding leap months (Qur'an 9:36-37).

Biographers like Ibn Ishaq record the month in which the events of Muhammad's life took place. Yet, Muhammad is never recorded doing anything on a leap month. Why is this?

  • I guess this is assuming the Arabs gave a special name to leap months rather than just repeating a month with the same name or something like that.
    – The Z
    Commented Nov 2, 2021 at 1:11
  • Your question has several assumptions which might not be true. There are other interpretations of what practice is described in 9:36-37 (such as postponing a sacred month) which does not have anything to do with adding a month. Secondly you assume that such a practice was continued in the early Islamic rule before 629, I would highly doubt that given how severely it is condemned. Most of the dated events in Seerah are about the period in Medinah under Islamic government.
    – UmH
    Commented Sep 7, 2022 at 3:23

1 Answer 1


The leap month had been inserted after about 3 years. It was called nasi. It's not to compensate the missing week day in the solar year (the week was already fixed to 7 days and asynchronous to the moon) but the lapse between the natural lunar month and the natural solar year, which is about 11 days.

The reason for not mentioning that month may be various:

Although it is not reported, it may be possible that the ancient Arabic leap month had a full name composed of the preceding month plus nasi, as it is common in the Jewish lunisolar calendar.

As the leap month was declared by the pagan religious authority, no leap month was introduced anymore after hijra. During the activity of the Prophet (p.b.u.h) before hijra, only 3, maybe 4 leap months were proclaimed. It's hence possible that nothing reported took place in that month and only in that month.

As the reports were written later, the timeline may have been interpolated in many cases, so that it seemed not compulsory to estimate that it fell in a leap month then deprecated.

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