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: Messenger of Allah, 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. (Using translation from Muslim 2735c)   

عَنِ النَّبِيِّ ﷺ أَنَّهُ قَالَ لَا يَزَالُ يُسْتَجَابُ لِلْعَبْدِ مَا لَمْ يَدْعُ بِإِثْمٍ أَوْ قَطِيعَةِ رَحِمٍ مَا لَمْ يَسْتَعْجِلْ قِيلَ يَا رَسُولَ اللهِ مَا الِاسْتِعْجَالُ؟ قَالَ يَقُولُ قَدْ دَعَوْتُ وَقَدْ دَعَوْتُ فَلَمْ يُسْتَجَبْ لِي فَيَسْتَحْسِرُ عِنْدَ ذَلِكَ وَيَدَعُ الدُّعَاءَ