اللَّهُمَّ لاَ سَهْلَ إِلاَّ مَا جَعَلْتَهُ سَهْلاً، وَأَنْتَ تَجْعَلُ الْحَزْنَ إِذَا شِئْتَ سَهْلاً
Allāhumma lā saḥla illā ma ja`altahu saḥla wa anta taj`alu ‘l-ḥazna idhā shi'ta saḥla. O Allah, there is no ease other than what You make easy. If You please You ease sorrow. Reference: Ibn Hibban in his Sahih (no. 2427), and Ibn As- Sunni (no. 351). Al-Hafidh (Ibn Hajar) said that this Hadith is authentic. It was also declared authentic by 'Abdul-Qadir Al-Arna'ut in his checking of An-Nawawi's Kitabul-Athkarp. 106.
Reference : Hisn al-Muslim 139