Prophet (Peace Be Upon Him) has said:
[Muslim, Book #035, Hadith #6595] "Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: The supplication of the servant is granted in case he does not supplicate for sin or for severing the ties of blood, or he does not become impatient. It was said: Allah's Messenger, what does:" If he does not grow impatient" imply? He said: That he should say like this: I supplicated and I supplicated but I did not find it being responded. and theu he becomes frustrated and abandons supplication."