From the reasons that prevent the servant from attaining the fulfillment of the supplication is his being hasty and impatient, so when the answer is delayed or slow in coming he becomes frustrated and gives up supplicating. This person is like the one who sows a seed or plants a flower, watering it and tending to it, then when it is delayed in appearing or flowering he leaves it and neglects it.
In Saheeh Bukhaaree from the hadeeth of Abu Hurayrah that the Messenger of Allaah (sallallaahu ’alayhi wa sallam) said, "your supplications will be answered as long as you are not impatient by saying, 'I have supplicated to my Lord but He has not answered.'" [Saheeh Bukhaaree [ Eng. Trans. 8/236 no. 352]]
In the Musnad of Ahmad from the hadeeth of Anas that the Messenger of Allaah (sallallaahu ’alayhi wa sallam) said, "the servant will always be in a state of good as long as he is not impatient." They asked, "how is he impatient?" He replied, "he says, 'I have supplicated to my Lord but he has not answered.'"
[Ahmad [3/193-210], Abu Ya`laa [no. 2865], at-Tabaraanee in 'al-Awsat' [no. 2518] and in 'ad-Du`aa' [no. 21], and ibn Adee [6/2219] Its isnaad is hasan and the hadeeth is also reported via another route from by al-Bazzaar [4/37].]