وَمَا كَانَ صَلَاتُهُمْ عِندَ ٱلْبَيْتِ إِلَّا مُكَآءً وَتَصْدِيَةً ۚ فَذُوقُوا۟ ٱلْعَذَابَ بِمَا كُنتُمْ تَكْفُرُونَ
Asad Quran Translation
and their prayers before the Temple are nothing but whistling and clapping of hands.35
Taste then, [O unbelievers,] this chastisement as an outcome of your persistent denial of the truth36
I.e., devoid of all spiritual contents. Some of the early authorities maintain that dancing around the Ka'bah, accompanied by whistling and hand-clapping, was actually a ritual practiced by the pre-Islamic Arabs. Although this explanation is quite plausible, it would appear from the context that the expression "whistling and clapping of hands" is used here metaphorically, to denote the spiritual emptiness of the religious rituals of people who are wont to attribute a quasi-divine efficacy to all manner of circumstantial "forces" - like wealth, power, social status, "luck", etc.
The chastisement or suffering referred to here was their crushing defeat at Badr.
Malik Quran Translation
Their prayer at the House of Allah is nothing but whistling and clapping of hands: whose only answer can be, "Taste the punishment because of your denying the truth."
Yusuf Ali Quran Translation
Their prayer at the house (of Allah) is nothing but whistling and clapping of hands: (its only answer can be) "taste ye the penalty because ye blasphemed."
Mustafa Khattab Quran Translation
Their prayer at the Sacred House was nothing but whistling and clapping. So taste the punishment for your disbelief.
Piktal Quran Translation
And their worship at the (holy) House is naught but whistling and hand clapping. Therefore (it is said unto them): Taste of the doom because ye disbelieve.
Wama kana salatuhum AAinda albayti illa mukaan watasdiyatan fathooqoo alAAathaba bima kuntum takfuroona