The Prophet (peace and blessings be upon him) said:
"It is disbelief on a man's part that he claims a lineage that is not known, or denies his own lineage, however insignificant it may be."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4486
Hadith Gradingالألبانی:حسن
Hadith Takhrij[هـ] عن ابن عمرو. الروض النضير ٥٨٧: الترغيب ٣/٨٨: حم، طص، طس.