The Jews transgress the Sanctity of the Sabbath
This Ayah explains Allah's statement,
وَلَقَدْ عَلِمْتُمُ الَّذِينَ اعْتَدَواْ مِنكُمْ فِى السَّبْتِ
(And indeed you knew those among you who transgressed in the matter of the Sabbath..) 2:65 Allah says to His Prophet here,
وَسْئَلْهُمْ
(And ask them) ask the Jews who are with you, about the story of their fellow Jews who defied Allah's command, so that His punishment overtook them all of a sudden for their evil actions, transgression and defiance by way of deceit. Also, warn the Jews (O Muhammad) against hiding your description that they find in their books, so that they do not suffer what their forefathers suffered. The village mentioned here is Aylah, on the shore of the Qulzum (Red) Sea. Muhammad bin Ishaq recorded from Dawud bin Al-Husayn from `Ikrimah that Ibn `Abbas commented on Allah's statement,
وَسْئَلْهُمْ عَنِ الْقَرْيَةِ الَّتِى كَانَتْ حَاضِرَةَ الْبَحْرِ
(And ask them about the town that was by the sea...) "A village called Aylah between Madyan and At-Tur (which is in Sinai). `Ikrimah, Mujahid, Qatadah and As-Suddi said similarly. Allah's statement,
إِذْ يَعْدُونَ فِى السَّبْتِ
(when they transgressed in the matter of the Sabbath;) means, they transgressed in the Sabbath and defied Allah's command to them to keep it sanctified,
إِذْ تَأْتِيهِمْ حِيتَانُهُمْ يَوْمَ سَبْتِهِمْ شُرَّعًا
(when their fish came to them openly on the Sabbath day,) visible on top of the water, according to Ad-Dahhak who reported it from Ibn `Abbas. Ibn Jarir said, "Allah's statement,
وَيَوْمَ لاَ يَسْبِتُونَ لاَ تَأْتِيهِمْ كَذَلِكَ نَبْلُوهُم
(and did not come to them on the day they had no Sabbath. Thus We made a trial of them,) means, this is how We tested them by making the fish swim close to the surface of the water , on the day which they were prohibited to fish. The fish would be hidden from them on the day when they were allowed to fish,
كَذَلِكَ نَبْلُوهُم
(Thus We made a trial for them,) so that We test them,
بِمَا كَانُواْ يَفْسُقُونَ
(for they used to rebel against Allah's command) by defying His obedience and rebelling against it." Therefore, these were a people who used a trick to violate Allah's prohibitions, taking an action that seemed legal on the surface. However, in reality, this action was meant to transgress the prohibition. Imam and scholar Abu `Abdullah Ibn Battah reported that Abu Hurayrah said that the Messenger of Allah ﷺ said,
«لَا تَرْتَكِبوُا مَا ارْتَكَبَتِ الْيَهُودُ فَتَسْتَحِلُّوا مَحَارِمَ اللهِ بِأَدْنَى الْحِيَل»
(Do not repeat what the Jews committed, and violate Allah's prohibitions using deceitful tricks.) This Hadith has a reasonable chain.
Tafsir Ibn Kathir (abridged, English).