Dua at the beginning of Ramadan
اللّهُـمَّ أَهِلَّـهُ عَلَيْـنا بِالأَمْـنِ وَالإيمـان، وَالسَّلامَـةِ...
اللّهُـمَّ أَهِلَّـهُ عَلَيْـنا بِالأَمْـنِ وَالإيمـان، وَالسَّلامَـةِ وَالإِسْلام، وَالتَّـوْفيقِ لِمَا تُحِـبُّ رَبَّنـا وَتَـرْضى، رَبُّنـا وَرَبُّـكَ الله
Allahumma ahillahu AAalayna bil-amni wal-eeman, wassalamati wal-islam, wattawfeeqi lima tuhibbu rabbana watarda, rabbuna wa-rabbuka Allah
Translation
O Allah, bring this moon over us with security, faith, peace and Islam, and in harmony with what our Lord loves and is pleased with. Our Lord and your Lord is Allah.
When to recite
Recited upon sighting the crescent moon of Ramadan. The same as the general crescent moon dua but said with special intention at the start of Ramadan.
Source / Reference
At-Tirmithi 5/504, Ad-Darimi 1/336