Is it permissible for a married woman to braid her hair with black or brown fabric threads, not with natural nor artificial hair? Please advise.

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

Scholars have unanimously agreed that women are prohibited from attaching human hair to their hair due to the generality of the authentic hadiths indicating the prohibition. For example, it was narrated that the Prophet, sallallaahu ‘alayhi wa sallam, said: "May Allaah curse women who attach hair (to the hair of others) and those who have it attached to theirs and women who pluck their eyebrows and those who ‎have it done." [Al-Bukhari and Muslim]

On the other hand, the scholars have held different opinions regarding attaching other than human hair to one's hair. In Al-Mughni, Ibn Qudaamah considered the most valid opinion to be that doing this is permissible. He said:

The most valid opinion is that what is forbidden is only to attach human hair to one's hair as it involves deception and to attach hair whose impurity is controversial. However, other types of hair extensions are not prohibited due to the absence of such considerations and because it achieves the consequent interest of a woman beautifying herself for her husband without any resulting harm.

In Al-Majmoo‘, An-Nawawi said: "Tying the hair with colored silk threads and so on, which do not resemble natural hair is not forbidden."

Thus, it is permissible for a woman to braid her hair using threads that do not resemble human hair. It is better to avoid black colors so that no deception is involved.

Allaah Knows best.