Rasullulah Sallalahu Allayhi Wassallam would make the following Supplication when the month of Rajab would approach:
اَللّهُمَّ بَارِكْ لَنَا فِيْ رَجَبَ وَشَعْبَانَ وَبَلِّغْنَا رَمَضَانَ
Allahumma barik lana fi Rajab wa Sha’baan wa ballighna Ramadhaan
‘‘O Allah ! Grant us Barakah (Blessing) during (the months of) Rajab and Sha’baan and allow us to reach Ramadhaan.’’
Shu’abul Imaan #3534, Ibnu Sunni #662,
Mukhtassar Zawaid Bazzar #662, Al Azkhaar #549