And if they argue with you, say:"Allah knows best what you do."This is like the Ayah:وَإِن كَذَّبُوكَ فَقُل لِّى عَمَلِى وَلَكُمْ عَمَلُكُمْ أَنتُمْ بَرِييُونَ مِمَّأ أَعْمَلُ وَأَنَاْ بَرِىءٌ مِّمَّا تَعْمَلُونَ And if they belie you, say:"For me are my deeds and for you are your deeds! You are innocent of what I do, and I am innocent of what you do!" (10:41)اللَّهُ أَعْلَمُ بِمَا تَعْمَلُونَAllah knows best of what you do.This is a stern warning and definite threat, as in the Ayah:هُوَ أَعْلَمُ بِمَا تُفِيضُونَ فِيهِ كَفَى بِهِ شَهِيداً بَيْنِى وَبَيْنَكُمْHe knows best of what you say among yourselves concerning it! Sufficient is He as a witness between me and you! (46:8)Allah says here:اللَّهُ يَحْكُمُ بَيْنَكُمْ يَوْمَ الْقِيَامَةِ فِيمَا كُنتُمْ فِيهِ تَخْتَلِفُونَ