When was the concept of "weekly day off" first introduced in Indian Subcontinent?

As one might expect, it is a tricky business to talk generally about practices on the Indian subcontinent. For most things that is as true today as it is for the subcontinent of centuries ago. The diversity of religions, cultures, languages, and the complex political realities over the centuries means that this answer really must be more of a sampling of the variety of practices.

Below I offer a sampling of what I have found on the practice of rest days in Indian Buddhism, Zoroastrianism, Jewish Indians, Hindu festivals, possibly regional rest days, and conclude with possible emergence of greater standardization with British colonial rule.

Uposatha and the Claim of Earliest Rest Days

The closest I came to something pointing to a very ancient origin is in an article by Bruce A. Kimball. I think this quote is also important because it points to the connection between feast days, taboos surrounding them, and rest days:

“Wandering in the desert where the moon so strongly stimulated the imagination of ancient peoples, the earliest Hebrews might have first declared periodic rest days of the lunar phase to be “unlucky” or “tabooed” and so recommended “abstinence and quiescence” in order not to incur the taboo. For example, this appears to be the origin of the upavasatha day of feasting for the ancient Aryans of India as well as the uposatha day of early Buddhists [1:306-7]

This connection, which traces the emergence of rest days in both the Buddhist uposatha (On Wikipedia) and Sabbath contexts again here in article by Edward Westermarck:

[Uposatha] is not only a day of rest, but has also from ancient times been a fast-day...the rest on the Sabbath was originally the consequence of that day being the festal and sacrificial day of the week, and only gradually became its essential attribute on account of the regularity with which it every eight day interrupted the round of everyday work. [3:411-2]

On when the Uposatha was held for Buddhists, with claim that it did not originate with Buddhists:

The Uposatha is a day of rest; it is not proper to trade or do any business; hunting and fishing are forbidden; schools and courts of justice are shut. It is also from ancient times a fasting day...” 8th and 14th or 15th of each half-month - Buddhism borrowed from other sects [2:99]

The Jewish population, especially on the west coast such as the Bene Israel, known as the Shanivar Telis (Saturday oil men?), keep to Saturday for their Sabbath [8:489]. The Zoroastrians in India have the interesting concept of intervals called Gahambars:

According to the Zoroastrian religion, the world was created in three hundred and sixty-five days, at six unequal intervals. At the end of each of these there was a day of rest. These intervals are called Gahambars, which fall six times in a year. On these occasions the Parsis follow the custom of the ancient Persians, who in their time gathered together and said prayers...custom is still followed as far as practicable in Bombay...The Mediozarem is the first of the six Gahambars and lasts for five days... [4:195]

Hindu Festivals and Regional Diversity

Elsewhere, everything I find shows incredible diversity. Here and there, but not in sources that seem to be particularly well researched, there is talk of Saturday as a weekly holy day, and some claim this corresponds to the traditional "oil bath" in parts of southern India, which could take many hours - something you can read about in Ashtanga yoga as well. However, I didn't find much in the way of detail.

Instead you find a lot of passages like this from Caleb Wright in 1853:

In India, the division of time into weeks has all along been observed. The remembrance, however, of the seventh as a Sabbath or sacred day of rest has been completely lost. Instead thereof, there have been substituted certain periodical anniversary days of high festival, in honor of the principal divinities...There is scarcely a day...which...is not celebrated by one or other of the leading sects... [7:201]

Others note local practices like Abbe DuBois in Mysore in 1906:

Many religious customs are followed only by certain sects...in the districts of Western Mysore that I have observed Monday in each week kept nearly in the same way as Sunday is among Christians. [9:20]

There are less frequent Hindu festivals that include days of rest, including:

• Pongal - Hindu festival on 14 January
• Ayudha Puja - day before Hindu festival of Dashahara in south India, containing a day of giving their tools of labor a rest [5:42,287]

And also some limited to certain tribes:

• Chapchar Kut - last day of the festival called Ziapur ni or "the day of rest after eating and drinking. On this day people would relax after hectic days of festivals” [6:242]
• Paul Kut - a harvest festival, followed by a Eipuar Awm Ni or the day of rest. [6:243]

I don't see much on the Muslim population. Globally speaking it looks like Jumu'ah on Friday (Wikipedia) , while a day of prayer and singled out, only really takes on its "rest day" in full form in some muslim countries in the process of modernization. I didn't find much on its application in pre-colonial India.

In the answer by @Kobunite we see the implementation of legally defined days of rest, but it looks like this process of Sundays being a customary day off starts to catch on during the course of the colonial period.

Ever since the British Government has been established in India, the people of this country have been accustomed to consider Sunday as the most convenient day of rest. No other day could now be selected which would not cause the greatest inconvenience to all concerned. [11:224]

An interview of a worker in Bombay from late 19th century also speaks of Sunday as the standard:

Sunday is the best day. Quite apart from any question of religion, this holiday has been observed for many years as a day of rest. [11:111]

The "first meeting of industrial workers in Bombay's history" in 1884 passed a resolution asking for a full day of rest on Sunday [10:328] and an "Act of 1891" made Sunday a day of rest in factories [11:230]

Overall, it would appear that in some areas or among some religious groups there are more regular festivals or religious days, with some cases of more frequent regular days of rest such as the observed weekly day of rest in Mysore, or the almost weekly Uposatha in some places like Sri Lanka, or the Gahambars of the Zoroastrians.

Sources

Sources are cited in format [Source Number:Page Number]

1. 1978 "The Origin of the Sabbath and Its Legacy to the Modern Sabbatical" Bruce A. Kimball Jstor

2. 1898 Manual Of Indian Buddhism Hendrik Kern Gbooks

3. 1907 "The Principles of Fasting" Edward Westermarck Jstor

4. 2004 Cultural and Religious Heritage of India: Zoroastrianism edited by Suresh K. Sharma, Usha Sharma Gbooks

5. 2006 The Religions of India: A Concise Guide to Nine Major Faiths by Roshen Dalal Gbooks

6. 2006 Encyclopaedia of Scheduled Tribes in India: In Five Volumes P. K. Mohanty Gbooks

7. 1853 India and Its Inhabitants Caleb Wright Gbooks

8. 2004 People of India: Maharashtra, Part 2 edited by B. V. Bhanu Gbooks

9. 1906 Hindu Manners, Customs and Ceremonies Abbe J. A. DuBois Gbooks

10. 1997 "Narayan Meghaji Lokhande: The Father of Trade Union Movement in India" Nalini Pandit Jstor

11. 1990 Labour Movement In India: Documents: 1891-1917, Volume 2 edited by S. D. Punekar, R. Varickayil Gbooks