This is the grave of Sarah (peace be upon her), the first wife of Ibrahim (peace be upon him) and the mother of Ishaq (peace be upon him). It is located in the south-eastern part of Masjid-e-Khalil.
The Prophet Ibrahim (peace be upon him) was 100 years old, and Sarah was 90 years old. They practically lost all hope of a problem in this old age, when the angel came to Ibrahim (peace be upon him) with the happy news of the birth of a wise son, his wife laughed and did not believe it.
She noted that she had passed the age, and now it was just silly to expect a child. The Quran tells us how this news was transmitted to Ibrahim (peace be upon him) and his wife in Sura Hud:
“And his wife, who was standing nearby, laughed when We gave her good news (about birth) of Ishaq and after Ishaq Yacoub” (Jacob) . She said, “Oh, woe is me! Shall I give birth to a child when I am an old woman, and this is my husband, an old man? Lo! This is a strange thing. They said: Do you wonder at the commandments of Allah? May the mercy of Allah and His blessings be with you, people of the Home! Lo! He is the Owner of Praise, Owner of Glory. ” [Quran 11: 71-73]
The Prophet Ishaq (peace be upon him) was born by the will of Allah.
Sarah (peace be upon her) was the daughter of the paternal uncle Ibrahim (peace be upon him). In At-Tareef wa Al-Alam, by Abu al-Qasim al-Suhayli is mentioned that when Sarah died (peace be upon her), Ibrahim (peace be upon him) married Qantura, the daughter of Yaqtan, and had six children from her; Madyan, Zamran, Sarj, Yaqshan and Nashq, while the sixth is not named. He married after her Hajun, the daughter of Amin, and she gave birth to five children; Kisan, Suraj, Ameem, Lutan and Nafis.
Source: Stories of the Prophets – Ibn Kathir