Surah Al-Anfal 8:35

وَمَا كَانَ صَلَاتُهُمْ عِندَ ٱلْبَيْتِ إِلَّا مُكَآءً وَتَصْدِيَةً ۚ فَذُوقُوا۟ ٱلْعَذَابَ بِمَا كُنتُمْ تَكْفُرُونَ

And their prayer at the House [i.e., the Kaʿbah] was not except whistling and handclapping. So taste the punishment for what you disbelieved [i.e., practiced of deviations].

Translation: Saheeh International

Tafsir

And their prayer at the Sacred House is nothing but whistling and hand-clapping in other words they do this in place of the prayer which they were ordered to perform — therefore taste now at Badr the chastisement for your unbelief!

Excerpt from Tafsir al-Jalalayn, commentary on 8:35, via Quran.com. The reader has the full commentary and 9 more tafsirs.