Nafi' (may Allah have mercy on him) said that he heard Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) supplicating on Safa, saying: "Allahumma innaka qulta: 'Ud'uni astajib lakum' [Surah Ghafir: 60], wa innaka la tukhlifu al-mi'ad [Surah Al Imran: 194], wa inni as'aluka kama hadaytani lil-Islami an la tanzi'ahu minni hatta tatawaffani wa ana muslim" (O Allah! You have said: 'Call upon Me; I will respond to you' [Surah Ghafir: 60], and 'You do not break the promise' [Surah Al Imran: 194]; and I ask You, just as You have guided me to Islam, not to take this Islam away from me until I die upon Islam).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9345