Reference : Hisn al-Muslim 175

اللهُ أَكْـبَر،
اللّهُمَّ أَهِلَّـهُ عَلَيْـنا بِالأمْـنِ وَالإيمـان،
والسَّلامَـةِ والإسْلام،
وَالتَّـوْفيـقِ لِما تُحِـبُّ رَبَّنـا وَتَـرْضـى، 
رَبُّنـا وَرَبُّكَ الله
Allāhu Akbar, 
Allāhumma ahillahu `alayna bi ‘l-amni wa ‘l-īmān,
was-salāmati wa ‘l-'Islām, 
wat-tawfīqi limā tuḥibbu Rabbanā wa tarḍā, 
Rabbunā wa Rabbukallāh.


Allah is the Most Great. 
O Allah, bring us the new moon with security and Faith, 
with peace and in Islam, 
and in harmony with what our Lord loves and what pleases Him. 
Our Lord and your Lord is Allah.

Reference:
At-Tirmidhi 5/504, Ad-Darimi 1/336. See also Al-Albani, Sahih At-Tirmidhi 
3/157.

Chapter: Upon sighting the crescent moon