When the Prophet of Allah ﷺ saw the new moon, he said: "a new moon of good and right guidance; a new moon of good and right guidance; a new moon of good and right guidance. I believe in Him Who created you" three times. He would then say: "Praise be to Allah Who has made such and such a month to pass and has brought such and such a month."
أَنَّ النَّبِيَّ ﷺ كَانَ إِذَا رَأَى الْهِلاَلَ قَالَ هِلاَلُ خَيْرٍ وَرُشْدٍ هِلاَلُ خَيْرٍ وَرُشْدٍ هِلاَلُ خَيْرٍ وَرُشْدٍ آمَنْتُ بِالَّذِي خَلَقَكَ ثَلاَثَ مَرَّاتٍ ثُمَّ يَقُولُ الْحَمْدُ لِلَّهِ الَّذِي ذَهَبَ بِشَهْرِ كَذَا وَجَاءَ بِشَهْرِ كَذَا