Musnad Ahmad 30:3182

I read to Abd al-Rahman: Malik, and Ishaq narrated to us, he said: Malik informed us, from Ibn Shihab, from Abu Ubayd, the freed slave of Ibn Azhar, from Abu Hurayrah, that the Messenger of Allah, may Allah bless him and grant him peace, said: "The supplication of one of you will be answered as long as he does not become hasty, saying: 'I have supplicated, but it has not been answered for me.'"