Book 20, Number 20.39.129:

Yahya related to me from Malik from Nafi that he heard Abdullah ibn Umar making dua on Safa saying, "O Allah, You have said, 'call on Me - I will answer you' and You do not break Your promise. So I am askingYou, in the same way that You have guided me to Islam, not to take it away from me, and that You make me die while I am muslim."