Tafseer Ibn Kathir of AL ANFAAL [35]

وَمَا كَانَ صَلاَتُهُمْ عِندَ الْبَيْتِ إِلاَّ مُكَاء وَتَصْدِيَةً فَذُوقُواْ الْعَذَابَ بِمَا كُنتُمْ تَكْفُرُونَ

And their prayer at the House was not except whistling and handclapping. So taste the punishment for what you disbelieved.