This house belonged to a Sahaabi names Arqam bin Abi Arqam
. For some time after Rasoolullah 
proclaimed his prophethood, this house was the secret centre of propagation. It was here that the Muslims gathered to perform Salaah and to learn about Islam.Daarul Arqam was therefore the first school in Islam.
It was after Umar
embraced Islam, that due to the acknowledgement of his valour and courage, Muslims began performing Salaah in the open and Islaam was propagated in public.The Abbasi Khalifah Haroon Ar-Rasheed had a Masjid built at this site (Daarul Arqam) in the year 171 A.H. (787). It is situated outside the Mas'aa, 36m east of Safa.
During their reigns, many Muslim Khulafaa have renovated and rebuilt the Masjid. However, when the Mas'aa was extended in 1375 A.H. (1955), the Masjid had to be made part of the Mas'aa and as a symbol of its location, a door is placed as one of the entrances (near the original site) named Baabu Daaril Arqam (Door of Daarul Arqam).
Sources:
Akhbaaru Makkah by Faakihi (vol 3, pg. 330),
Az Zuhoor Muqtatifah (pg. 100)
Tareekhul Qawmm (vol 2, pg. 82, vol 3 pg. 436)
Jaami'ul Lateef (pg. 204)
