Reference: Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa., – Volume 5, Page 193, Question 10 of Fatwa No.9850
Fataawa wa Ahkaam fee Sha’r an-Nisaa – Question 5, Page 8
Question: What is the ruling regarding a woman having hair extensions?
Response: It is haraam for a woman to have hair extensions using [real] hair or that which resembles [real] hair for the authentic evidences which mention this [prohibition].
And with Allaah lies all success and may Allaah send prayers and salutations upon our Prophet (sal-Allaahu ‘alayhi wa sallam) and his family and his companions.