Sunnah.com reference : Book 8, Hadith 215English translation : Book 8, Hadith 1161Arabic reference : Book 8, Hadith 1150
Narrated Bahz bin Hakim on his father's authority from his grandfather (RA):
I asked, "O Allah's Messenger, to whom should I be kind and dutiful?" He replied, "Your mother." I asked, "Who comes next?" He replied, "Your mother." I asked, "Who comes next?" He replied, "Your mother." I asked, "Who comes next?" He replied, "Your father, then your relatives in order of nearness (of relationship)."

[Abu Dawud and at-Tirmidhi reported it; the latter graded it Hasan (good)].
وَعَنْ بَهْزِ بْنِ حَكِيمٍ, عَنْ أَبِيهِ, عَنْ جَدِّهِ قَالَ: { قُلْتُ: يَا رَسُولَ اَللَّهِ! مَنْ أَبَرُّ? قَالَ: "أُمَّكَ".‏ قُلْتُ: ثُمَّ مِنْ? قَالَ: "أُمَّكَ".‏ قُلْتُ: ثُمَّ مِنْ "? قَالَ: "أُمَّكَ".‏ قُلْتُ: ثُمَّ مِنْ? قَالَ: "أَبَاكَ, ثُمَّ اَلْأَقْرَبَ فَالْأَقْرَبَ".‏ }  أَخْرَجَهُ أَبُو دَاوُدَ, وَاَلتِّرْمِذِيُّ وَحُسَّنَهُ  1‏ .‏‏1 ‏- حسن.‏ رواه أبو داود (5139)‏، والترمذي، (1897)‏، وقال الثاني: "حديث حسن".‏