Hagar plays a very important role in the identity of the Arab people as a mother of Ishmael she is considered to be mother of all Arabs. The prophet Muhammad was a direct descendant of Ishmael from the line of Kedar one of Ishmael's sons.
Sahih Bukhari 4.577-578; Sahih Bukhari 7.21
The tyrant then gave Hajar as a girl-servant to Sarah. Sarah came back
(to Ibrahim) while he was praying. Ibrahim, gesturing with his hand,
asked, "What has happened?" She replied, "Allah has spoiled the evil
plot of the infidel and gave me Hajar for service." Abu Huraira then
addressed his listeners saying, "That (Hajar) was your mother, O you Arabs, the descendants of Ishmael, Hajar's son".
Ibrahim, Hagar and Ishmael in Islam:
Ishmael was born, Sarah felt jealous and when she finally conceived and
had given birth to Isaac, she asked Abraham to to send Hagar and her
son away. Abraham complied and sent Hagar and Ishmael to a barren desert
known as Makkah. But Abraham was very troubled about this and also
missed his son Ismael and wife Hagar. So he returned to the place he left them and prayed to God teh following prayer:
"Our Lord, I have settled some of my descendants in an uncultivated valley near Your sacred House, our Lord, that they may establish prayer. So make hearts among the people incline towards them and provide for them from the fruits that they may be grateful."
(Surat 'Ibrahim 14:37 Sahih International)