It was narrated that ‘Ali said:
“When the following was revealed: “And Hajj (pilgrimage to Makkah) to the House (Ka’bah) is a duty that mankind owes to Allah, for whoever can bear the way.” [3:97] They asked: ‘O Messenger of Allah, is Hajj every year?’ He remained silent. They asked: ‘Is it every year?’ He said: ‘No. If I had said yes, it would have become obligatory.’ Then the following was revealed: “O you who believe! Ask not about things which, if made plain to you, may cause you trouble.’” [5:101]

حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ نُمَيْرٍ، وَعَلِيُّ بْنُ مُحَمَّدٍ، قَالاَ حَدَّثَنَا مَنْصُورُ بْنُ وَرْدَانَ، حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ الأَعْلَى، عَنْ أَبِيهِ، عَنْ أَبِي الْبَخْتَرِيِّ، عَنْ عَلِيٍّ، قَالَ لَمَّا نَزَلَتْ {وَلِلَّهِ عَلَى النَّاسِ حِجُّ الْبَيْتِ مَنِ اسْتَطَاعَ إِلَيْهِ سَبِيلاً}. قَالُوا يَا رَسُولَ اللَّهِ الْحَجُّ فِي كُلِّ عَامٍ فَسَكَتَ ثُمَّ قَالُوا أَفِي كُلِّ عَامٍ فَقَالَ " لاَ وَلَوْ قُلْتُ نَعَمْ لَوَجَبَتْ " . فَنَزَلَتْ {يَا أَيُّهَا الَّذِينَ آمَنُوا لاَ تَسْأَلُوا عَنْ أَشْيَاءَ إِنْ تُبْدَ لَكُمْ تَسُؤْكُمْ }.