"When Allah revealed: And Hajj to the House is a duty that mankind owes to Allah, for whomever is able to bear the journey. They said: 'O Messenger of Allah! Is that every year?' He remained silent. So they said: 'O Messenger of Allah! Is that every year?' He said: 'No. If I had said yes, then it would have been made obligatory.' So Allah revealed: O you who believe! Do not ask about things which, if made plain to you, may cause you trouble.  

لَمَّا نَزَلَتْ ( وَلِلَّهِ عَلَى النَّاسِ حِجُّ الْبَيْتِ مَنِ اسْتَطَاعَ إِلَيْهِ سَبِيلاً ) قَالُوا يَا رَسُولَ اللَّهِ أَفِي كُلِّ عَامٍ فَسَكَتَ فَقَالُوا يَا رَسُولَ اللَّهِ أَفِي كُلِّ عَامٍ قَالَ لاَ وَلَوْ قُلْتُ نَعَمْ لَوَجَبَتْ فَأَنْزَلَ اللَّهُ (يَا أَيُّهَا الَّذِينَ آمَنُوا لاَ تَسْأَلُوا عَنْ أَشْيَاءَ إِنْ تُبْدَ لَكُمْ تَسُؤْكُمْ ) قَالَ وَفِي الْبَابِ عَنِ ابْنِ عَبَّاسٍ وَأَبِي هُرَيْرَةَ