﴿ وَمَا كَانَ صَلَاتُهُمْ عِندَ ٱلْبَيْتِ إِلَّا مُكَآءًۭ وَتَصْدِيَةًۭ ۚ فَذُوقُوا۟ ٱلْعَذَابَ بِمَا كُنتُمْ تَكْفُرُونَ ﴾

“and their prayers before the Temple are nothing but whistling and clapping of hands. Taste then, [O unbelievers,] this chastisement as an outcome of your persistent denial of the truth!”

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!