Riyad as-Salihin 1499
Abu Hurairah (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ), "The supplication of every one of you will be granted if he does not get impatient and say (for example): 'I supplicated my Rubb but my prayer has not been granted'." [Al-Bukhari and Muslim] . The narration of Muslim is: "The supplication of a slave continues to be granted as long as he does not supplicate for a sinful thing or for something that would cut off the ties of kinship and he does not grow impatient." It was said: "O Messenger of Allah! What does growing impatient mean?" He (ﷺ) said, "It is one's saying: 'I supplicated again and again but I do not think that my prayer will be answered.' Then he becomes frustrated (in such circumstances) and gives up supplication altogether."
وعنه أن رسول الله صلى الله عليه وسلم قال‏:‏ ‏
"‏يستجاب لأحدكم ما لم يعجل‏:‏ يقول‏:‏ قد دعوت ربي، فلم يستجب لي‏"‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏ وفي رواية لمسلم لا يزال يستجاب للعبد ما لم يدعُ بإثم أو قطيعة رحم ما لم يستعجل‏.‏ قيل يا رسول الله ما الاستعجال‏؟‏ قال يقول قد دعوت وقد دعوت فلم أرَ من يستجب لي فيستحسر عند ذلك ويدع الدعاء‏.‏