Source: Fatwa Online : The ruling regarding hair extensions
Question: What is the ruling regarding a woman having hair extensions?
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 `alayhe wa sallam) and his family and his companions.
The Permanent Committee for Islaamic Research and Fataawa
Head: Shaykh ‘Abdul ‘Azeez Ibn Abdullaah Ibn Baaz;
Deputy Head: Shaykh ‘Abdur-Razzaaq ‘Afeefee;
Member: Shaykh ‘Abdullaah Ibn Ghudayyaan
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
Bukhari :: Book 7 :: Volume 72 :: Hadith 817
Narrated 'Aisha :
An Ansari girl was married and she became sick and all her hair fell out intending to provide her with false hair. They asked the Prophet who said, "Allah has cursed the lady who artificially lengthens (her or someone else's) hair and also the one who gets her hair lengthened."