This curtain is almost certainly the covering to the Bab al-Tawbah (Door of Repentance), the door which opens on some stairs which lead to a place where the idols were kept in pagan times before the Prophet Muhammad had them removed and destroyed. In later times this sacred area was used as a treasury for precious gifts to the shrine from various Muslim rulers. It is distinguished from the curtain which covers the outer door, which is more than twice the size and always has a split in the middle to allow passage through it.
The inscriptions are all Qur'anic and read as follows:
I And we covenanted with Abraham and Isma'il that they should sanctify my House from sura al-Baqarah, II v. 125
II (Take four birds, tame them to turn to....) ...thee; put a portion of them on every hill, and call them: they will come to thee with speed. from sura al-Baqarah, II v. 260
III Whoever enters it attains security; pilgrimage therto is a duty men owe to God -those who can afford the journey from sura al-'Imran, III v. 97
IV ..When Abraham raised the foundations of this house and also Isma'il and they prayed.., sura al-Baqarah, II v. 127
A very similar curtain is in the Tareq Rajab collection in Kuwait. It also contains the first three Qur'an extracts, but the lower portion contains the genealogy of the Ottoman Sultan Abdulhamid II, and is dateable to the end of the 19th century. It is highly likely that the present curtain was made at around the same time. (Safawat,N.F.: The harmony of letters, Singapore, 1997, pp. 114-5)