Alqamah and al-Aswad both said that Abdullah bin Mas'ud (may Allah be pleased with him) stood at the edge of Safa, and a man said: O Abu Abd al-Rahman! Here? He said: By the One besides whom there is no god, this is the standing place of the one upon whom Surah al-Baqarah was revealed.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9350