How can I differ from the Jews on the days that they venerate?
Question

How can I differ from the Jews on the days that they venerate? Is that done by fasting, because fasting means that the day is not a festival (eid)? Or is it by not fasting and not aiming to fast on that day? Regarding the first idea, there is the hadith of Umm Salamah: The Messenger of Allah (blessings and peace of Allah be upon him) used to fast on Saturdays and Sundays more than on other days, and he would say: “They are two festival days (eids) of the polytheists, and I like to differ from them.” And regarding the second idea, the scholars give as the reason for that the fact that the Prophet (blessings and peace of Allah be upon him) forbade fasting on Saturdays.
Praise be to Allah.What is known from the teachings of Islam, in which the texts of the Quran and Sunnah were narrated via many chains of narration, is that it is not permissible to imitate the disbelieving nations in what is unique to them of actions, beliefs, words and appearance.
It is well known that not imitating them may be achieved by not following them and not doing things that are uniquely theirs.
That includes their festivals, so differing from them and not imitating them may be achieved simply by not venerating those festivals and not celebrating them. If the Muslim achieves that and ignores celebrating those days, or avoids singling them out for some activities, then in that case he will have managed to differ from them.
It was narrated in the hadith of Anas: When the Messenger of Allah (blessings and peace of Allah be upon him) came to Madinah, they had two days on which they used to play. He said: “What are these two days?” They said: We used to play on these days during the Jahiliyyah. The Messenger of Allah (blessings and peace of Allah be upon him) said: “Allah has replaced them for you with something better than them: the Day of [Eid] al-Adha and the day of [Eid] al-Fitr.” Narrated by Abu Dawud (1134); classed as sahih by al-Albani in as-Silsilah as-Sahihah (2021).
Thus the Prophet (blessings and peace of Allah be upon him) instructed them to give up celebrating those two days as festivals, but he did not instruct them to do anything more than that, such as fasting and the like, in order to differ from the polytheists.
Ash-Shatibi (may Allah have mercy on him) said:
The second type is matters in which the Lawgiver did not give a specific ruling, or overlooked some matters where there is a reason now, and there was a reason at the time of revelation and afterwards, but no instruction was given in addition to what was there at that time.
When the Lawgiver overlooks such matters, it is like stating that the shar‘i objective concerning that matter should not be extended beyond the general rulings concerning such matters, nor should it be reduced, because when there was a reason [at the time of the Prophet (blessings and peace of Allah be upon him)] to dictate a practical, specific ruling, yet the Lawgiver did not legislate such a ruling or indicate that it should be worked out, this makes it clear that anything additional to what was narrated in the religious texts is an innovation (bid‘ah) that has been added and is contrary to the objectives of the Lawgiver, as it may be understood that the Lawgiver intended that we should stop at that limit and not add anything to it or take anything away from it."(Al-I‘tisam 2/282).
What we may understand from the above is that deliberately fasting to confirm that we are different from them is something that is not prescribed, and a number of scholars have stated that it is disliked (makruh) to do so, because paying attention to it and waiting for that day to come every year in order to fast is a kind of venerating it.
Ibn al-Qayyim (may Allah have mercy on him) said:
If it is said: What do you say about fasting on the days of Nowruz, Mahrajan and other festivals of the polytheists?
The answer is: Many of the scholars regarded that as disliked (makruh) and most of the companions of Ahmad also thought that it is disliked.
Ahmad said, according to a report narrated by his son ‘Abdullah: Waki‘ told us, from Sufyan, from a man, from Anas and al-Hasan, that they disliked fasting on the days of Nowruz and Mahrajan. ‘Abdullah said: My father said: The man [mentioned in the isnad] is Aban ibn Abi ‘Ayyash. When Ahmad gave this answer to the one who asked him about fasting on these two days, this indicates that this was his favoured view. This is one of the two views narrated by his companions regarding such matters.
And it was said that this was not his favoured view, and the view that he narrated is not to be attributed to him. Most of his companions were of the view that it is disliked, and they gave as the reason for that the fact that these are two days that are venerated by the disbelievers, so singling them out from among other days for fasting means going along with the disbelievers in their veneration of these days, so it is disliked [to fast on those two days], as is also the case with regard to Saturday. The author of al-Mughni said: By analogy with this, the same ruling applies to all the festivals of the disbelievers or any day that they single out for veneration."(Hashiyat Ibn al-Qayyim ma‘a ‘Awn al-Ma‘bud  7/52).
Secondly:
With regard to the hadith of Kurayb the freed slave of Ibn ‘Abbaas, in which he says that he heard Umm Salamah say: The Messenger of Allah (blessings and peace of Allah be upon him) used to fast on Saturdays and Sundays more than on other days, and he would say: “They are two festival days (eids) of the polytheists, and I like to differ from them.” Narrated by Ahmad in al-Musnad (44/330-331); al-Hakim in al-Mustadrak (1/436) – he said: Its isnad is sahih, and adh-Dhahabi did not comment on it.
Ibn al-Qayyim (may Allah have mercy on him) said in Zad al-Ma‘ad (2/74-75): There are some reservations about the soundness of this hadith.
Al-Albani classed it as da‘if (weak) in Silsilat al-Ahadith ad-Da‘ifah (3/219).
Hence we may note the following:
1.. There is a difference of scholarly opinion as to the soundness of this hadith. It also contradicts another hadith concerning the soundness of which the scholars differed. It is the hadith which says that the Prophet (blessings and peace of Allah be upon him) said: “Do not fast on Saturdays except what is obligatory for you.” Narrated by Abu Dawud (2421), at-Tirmidhi (744) and Ibn Majah (1726).
Because of this scholarly difference of opinion, this hadith cannot be taken as a basic principle which applies to every festival of the disbelievers.
2.. Even if we assume that the hadith is sahih, we cannot apply it to all the festivals of the disbelievers, because the Prophet (blessings and peace of Allah be upon him) lived alongside the Jews in Madinah and alongside Christians and polytheists in the Arabian Peninsula, and undoubtedly they had a number of festivals and days that they venerated throughout the year, but it is not known that the Prophet (blessings and peace of Allah be upon him) was keen to fast on the days of their festivals (eids) in order to openly differ from them, apart from Saturdays and Sundays.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
Any act of worship that was not prescribed, even though there may have been a reason for it to be done and there was no impediment to that, may be understood as being prohibited."(Iqtida’ as-Sirat al-Mustaqim  2/721).
3.. Some of the scholars thought that in order to reconcile between the texts, it may be noted that regarding the festivals of the disbelievers of which the dates are worked out according to the Arabian calendar, it is recommended (mustahabb) to differ from them by fasting on those days, following the hadith of Umm Salamah. As for festivals of which the dates are worked out according to calendars other than the Arabian calendar, it is not recommended to fast on those days.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
It may be said that it is disliked (makruh) to fast on the days of Nowruz and Mahrajan, and similar days of which the dates are not worked out according to the Arabian calendar, in contrast to what is mentioned in the hadith about Saturdays and Sundays, because if a person aims to fast on the days of non-Arab or jahili festivals, that may lead to doing some rituals on those days and reviving them and making them known, in contrast to Saturdays and Sundays, which are known in the Muslim calendar, and there are no negative consequences to fasting on those days. Thus it is recommended (mustahabb) to fast on the days of their festivals that are known according to the Islamic, Arabian calendar, but it is disliked (makruh) to do so with regard to festivals of which the dates are worked out according to non-Arab, jahili calendars, so that we may reconcile between the hadiths. And Allah knows best."(Iqtida’ as-Sirat al-Mustaqim  2/580).
Therefore, according to this view also, it is still disliked (makruh) to fast on the festivals of the disbelievers, apart from Saturdays and Sundays, because the dates of the festivals of the disbelievers that are well known today are not worked out according to the Islamic calendar.
And Allah knows best.