اللَّهُمَّ أَهِلَّهُ عَلَيْنَا بِالْأَمْنِ وَالْإِيمَانِ وَالسَّلَامَةِ وَالْإِسْلَامِ
What this dua means
It welcomes each new lunar month with a prayer for safety and faith.
When to read it
Say it when you sight the new crescent moon.
Its virtue
It follows the Prophet's habit of turning every new month into a fresh start with Allah.
getsalahtime.com