The Shulchan Arukh (O.C. 672:2), based on the Tur, rules that after the Chanukah candles have burned for the minimum required period – a half-hour – one may extinguish the candles, or derive personal benefit from the light. Although Halakha forbids making personal use of the candles during the first half-hour after they are lit, they may be used for personal benefit after they have burned for this period in fulfillment of the mitzva.
As the author of the Shulchan Arukh himself notes in Beit Yosef (O.C. 677), this halakha seems to contradict the halakha noted by the Rosh (Shabbat 2:9) regarding the oil that remains in the lamps after the final night of Chanukah. The Rosh cited the ruling of the She’iltot that this oil may not be used or simply discarded, as it is considered sacred, and it must therefore be burned. This would seem to prove that the Chanukah lights are deemed halakhically sacred even beyond the minimum half-hour of burning, as the leftover oil after the eighth night is forbidden for ordinary use.
The Beit Yosef suggests two approaches to reconcile these rulings. First, he distinguishes between oil that was left over after the candles burned for a half-hour, which is entirely permissible for use, and oil left over when the candles, for whatever reason, were extinguished before burning for a half-hour. The She’iltot’s ruling applies specific to this situation, where the leftover oil is oil that was to have been used for the requirement of kindling the Chanukah lights for a half-hour. This oil is, indeed, sacred, and may not be used for personal benefit. The Beit Yosef follows this approach in the Shulchan Arukh (677:4), where he rules that leftover oil that was needed for the minimum required period when the Chanukah candles were to burn may not be used for personal benefit. The clear implication is that if the candles on the eighth night burned for a half-hour or more, the leftover oil is not forbidden for benefit.
However, the Beit Yosef also cites a different view, that of Mahari Abuhav, who drew a different distinction – between one who placed oil in the lamps with the intention that the lamps should burn for only a half-hour, and one who placed oil in the lamps without such intention. If one intended for the candles to burn for only a half-hour, then after a half-hour, one may derive benefit from them. If, however, one prepared the lamps without any specific intention, then all the oil in the lamps is forbidden for personal use, and for this reason leftover oil after Chanukah is forbidden.
Mahari Abuhav’s explanation gives rise to the question of why the extra oil is deemed halakhically sacred. If only one half-hour’s worth of oil is needed for the performance of the mitzva, why is the excess endowed with halakhic significance?
One explanation is offered by Maharim Shick, in his work on Sefer Ha-mitzvot (98). He suggests that if one uses a large lamp for the Chanukah lights, then one enhances the mitzva by filling the cups with oil, which has the effect of producing a larger, stronger flame. Therefore, even the additional oil is endowed with halakhic sanctity unless one specifically intends to sustain the candles for just the minimum required duration.
Rav Asher Weiss explains Mahari Abuhav’s view more simply, claiming that he likely felt that there is value in having the Chanukah candles burn beyond the minimum required duration. For one thing, Rav Weiss writes, it is possible that Mahari Abuhav refers to the custom to light Chanukah candles indoors due to the dangers entailed in lighting outdoors as Halakha optimally requires. If one is already lighting indoors, then it stands to reason that pirsumei nisa – the publicizing of the miracle – is achieved well beyond the half-hour after nightfall when Chazal estimated that people are still found outdoors. Since people are present and awake in the home well after dark, it is worthwhile to have the candles burn well into the night. Therefore, there is value in supplying the candles with oil to burn for longer than just a half-hour, and thus this extra oil is deemed sacred. And even if one lights outdoors, Rav Weiss suggests, it is possible that, at least in the view of Mahari Abuhav, one enhances the mitzva if he resides in a time and place when people are outdoors even later than a half-hour after nightfall. For this reason, perhaps, Mahari Abuhav felt that even the additional oil, which sustains the candles beyond the period of a half-hour, is endowed with halakhic sanctity, as it facilitates the publicizing of the miracle, albeit beyond that which Halakha strictly requires.