Sahih Muslim 2358aBook 43, Hadith 174
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 " .
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.