كتاب الفضائل
43
The Book of Virtues
(37)
Chapter: Respecting Him And Not Asking Him Unnecessary Questions
(37)
باب تَوْقِيرِهِ صلى الله عليه وسلم وَتَرْكِ إِكْثَارِ سُؤَالِهِ عَمَّا لاَ ضَرُورَةَ إِلَيْهِ أَوْ لاَ يَت
Sahih Muslim 2358 a

Amir b. Sa'd reported on the authority of his father that Allah's Messenger (ﷺ) said:

The greatest sinner amongst the Muslims is one who asked about a thing (from Allah's Apostle) which had not been forbidden for the Muslims and it was forbidden for them because of his persistently asking about it.
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، أَخْبَرَنَا إِبْرَاهِيمُ بْنُ سَعْدٍ، عَنِ ابْنِ شِهَابٍ، عَنْ عَامِرِ بْنِ، سَعْدٍ عَنْ أَبِيهِ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ إِنَّ أَعْظَمَ الْمُسْلِمِينَ فِي الْمُسْلِمِينَ جُرْمًا مَنْ سَأَلَ عَنْ شَىْءٍ لَمْ يُحَرَّمْ عَلَى الْمُسْلِمِينَ فَحُرِّمَ عَلَيْهِمْ مِنْ أَجْلِ مَسْأَلَتِهِ ‏"‏ ‏.‏
Reference : Sahih Muslim 2358 a
In-book reference : Book 43, Hadith 174
USC-MSA web (English) reference : Book 30, Hadith 5821
  (deprecated numbering scheme)