اَللَّهُمَّ بَارِكْ لَنَا فِي رَجَبٍ وَشَعْبَانَ، وَبَلِّغْنَا رَمَضَانَ
Transliteration
Allahumma barik lana fi Rajabin wa Sha'bana, wa ballighna Ramadan
English meaning
O Allah, bless for us Rajab and Sha'ban, and let us reach Ramadan.
When is it recited?
Starting from the month of Rajab.
Source
al-Tabarani, al-Mu'jam al-Awsat, IV/189; Ahmad ibn Hanbal, Musnad, I/259. Its chain is weak; it may be recited as a dua.