Urwah bin al-Zubayr (may Allah have mercy on him) narrates from a woman of Banu al-Najjar (may Allah be pleased with her) that she said: My house was near the masjid and taller than the other houses, and Sayyiduna Bilal (may Allah be pleased with him) used to give the Fajr adhan from it. He would come before dawn, sit on the house and watch for the dawn; when he saw it, he would stretch himself and then say: 'Allahumma inni ahmaduka wa asta'inuka 'ala Quraysh an yuqimu dinak' (O Allah, I praise You and seek Your help concerning Quraysh, that they may establish Your religion). Then he would give the adhan. She said: By Allah, to my knowledge he did not leave these words for a single night.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1995