Yahya related to me from Malik that Zayd ibn Aslam used to say, "No-one makes a dua without one of three things happening. Either it is answered, or it is stored up for him, or wrong actions are atoned for by it."
أَنَّهُ كَانَ يَقُولُ مَا مِنْ دَاعٍ يَدْعُو إِلاَّ كَانَ بَيْنَ إِحْدَى ثَلاَثٍ إِمَّا أَنْ يُسْتَجَابَ لَهُ وَإِمَّا أَنْ يُدَّخَرَ لَهُ وَإِمَّا أَنْ يُكَفَّرَ عَنْهُ