أَخْبَرَنَا مُحَمَّدُ بْنُ الْعَلاَءِ، قَالَ حَدَّثَنَا أَبُو مُعَاوِيَةَ، عَنِ الأَعْمَشِ، عَنْ عُمَارَةَ، هُوَ ابْنُ عُمَيْرٍ عَنْ عَبْدِ الرَّحْمَنِ بْنِ يَزِيدَ، قَالَ أَكْثَرُوا عَلَى عَبْدِ اللَّهِ ذَاتَ يَوْمٍ فَقَالَ عَبْدُ اللَّهِ إِنَّهُ قَدْ أَتَى عَلَيْنَا زَمَانٌ وَلَسْنَا نَقْضِي وَلَسْنَا هُنَالِكَ ثُمَّ إِنَّ اللَّهَ عَزَّ وَجَلَّ قَدَّرَ عَلَيْنَا أَنْ بَلَغْنَا مَا تَرَوْنَ فَمَنْ عَرَضَ لَهُ مِنْكُمْ قَضَاءٌ بَعْدَ الْيَوْمِ فَلْيَقْضِ بِمَا فِي كِتَابِ اللَّهِ فَإِنْ جَاءَ أَمْرٌ لَيْسَ فِي كِتَابِ اللَّهِ فَلْيَقْضِ بِمَا قَضَى بِهِ نَبِيُّهُ صلى الله عليه وسلم فَإِنْ جَاءَ أَمْرٌ لَيْسَ فِي كِتَابِ اللَّهِ وَلاَ قَضَى بِهِ نَبِيُّهُ صلى الله عليه وسلم فَلْيَقْضِ بِمَا قَضَى بِهِ الصَّالِحُونَ فَإِنْ جَاءَ أَمْرٌ لَيْسَ فِي كِتَابِ اللَّهِ وَلاَ قَضَى بِهِ نَبِيُّهُ صلى الله عليه وسلم وَلاَ قَضَى بِهِ الصَّالِحُونَ فَلْيَجْتَهِدْ رَأْيَهُ وَلاَ يَقُولُ إِنِّي أَخَافُ وَإِنِّي أَخَافُ فَإِنَّ الْحَلاَلَ بَيِّنٌ وَالْحَرَامَ بَيِّنٌ وَبَيْنَ ذَلِكَ أُمُورٌ مُشْتَبِهَاتٌ فَدَعْ مَا يَرِيبُكَ إِلَى مَا لاَ يَرِيبُكَ‏.‏ قَالَ أَبُو عَبْدِ الرَّحْمَنِ هَذَا الْحَدِيثُ جَيِّدٌ جَيِّدٌ‏.‏

It was narrated that 'Abdur-Rahman bin Yazid said: "The people asked 'Abdullah too many questions one day, and 'Abdullah said: 'There was a time when we did not pass so many judgments, but now that time is over. Now Allah, the Mighty and Sublime, has decreed that we reach a time when, as you see, (we are asked to pass many judgments). Whoever among you is asked to pass a judgment after this day, let him pass judgment according to what is in the Book of Allah. If he is faced with a matter that is not mentioned in the Book of Allah, let him pass judgment according to the way His Prophet [SAW] passed judgment. If he is faced with a matter that is not mentioned in the Book of Allah and concerning which His Prophet did not pass judgment, then let him pass judgment according to the way the righteous passed judgment. If he is faced with a matter that is not mentioned in the Book of Allah, and concerning which His Prophet and the righteous did not pass judgment, then let him strive to work it out, and let him not say 'I am afraid, I am afraid.' For that which is lawful is clear and that which is unlawful is clear, and between them are matters which are not as clear. Leave that which makes you doubt for that which does not make you doubt.'" Translation Not Available

Book reference: Sunan An Nisai Book 49 Hadith 5397
Web reference: Sunan An Nisai Volume 6 Book 49 Hadith 5399