The Hijr Ismail (Hateem) is a crescent-shaped area situated just adjacent to the Holy Kabah. A part of Hijr (Hateem) is also known as Hijr-Ismail which means Stone for Ismail, which is the place where a shelter was made by Ibrahim for his wife Hagar and son Ismail.
Pilgrims don’t make tawaf or move in the region between this divider and the Ka’bah. This is 90 cm in stature and 1.5 m in width and of white marble.
1- Hijr Ismail is a low divider, which was a part of Kabah when Abraham built it initially. It is said that approximately 3 meters of the area adjacent to the wall of Hijr (Hateem) are considered to be a part of Kabah so tawaf must be performed outside the finish range of the Hijr (Hateem).
2- Later on, Kabah was reconstructed by Quraysh, during which the Kabah took its cubical shape and Hijr (Hateem) was left outside. It is a semi-circular, crescent-shaped low wall adjacent to Kabah.
Some researchers said that the graves of Ismail and his mother Hajar lie covered underneath the Hijr Ismail. However, others have rejected those narrations as weak.
3- At the age of 35 years of Prophet (PBUH), a disastrous flood harmed the Kabah, which was already weakened previously by a huge fire, and was at risk of destruction.
Feeling the need to protect the house of worship, the Quraysh chose to modify and rebuilt the Kabah and did every possible thing for the development. There was a shipwrecked nearby, and so its wood was brought into use. The wood worker named Baqoom developed the dividers of the Kabah.
The Prophet (PBUH) and his Uncle Abbas were around the work for nobles. Little dividers were assembled demonstrating the first limits of the establishment laid down by the Prophet Ibrahim, which was an encased territory over the northern side of Haram/ Kabah.
“I liked to enter the House (the Ka’bah) and pray therein. The Messenger of Allah caught me by hand and admitted me to al-Hijr (Hateem). He then said:
Pray in al-Hijr (Hateem) when you intend to enter the House (the Ka’bah), for it is a part of the House (the Ka’bah). Your people shortened it when they built the Ka’bah, and they took it out of the House. (Sunan Abi Dawud 2028)
5- Aisha said:
”I said: ‘O Messenger of Allah! Can I not enter the House?’
He said:
Enter the Hijr (Hateem) for it is part of the House. (Sunan an-Nasa’i 2911)
6- Narrated Hazrat Jabir bin `Abdullah that he heard Allah’s Messenger saying:
When the people of Quraish did not believe me (i.e. the story of my Night Journey), I stood up in Al-Hijr (Hateem) and Allah displayed Jerusalem in front of me, and I began describing it to them while I was looking at it. (Sahih Al-Bukhari 3886)
7- Aisha heard Allah’s Messenger as saying:
If your people, had not been recent converts to Islam, I would have spent the treasure of the Ka’bah in the way of Allah and would have constructed its door just on the level of the ground and would have encompassed in it the space of Hijr (Hateem). (Sahih Muslim 1333 d)
Source: http://lifeinsaudiarabia.net.