When the Prophet sighted the moon of Rajab i.e. two months before Ramadan...he used to pray to Allah in the following words:
اَللّهُمَّ بَارِكْ لَنَا فِى رَجَبَ وَ شَعْبَانَ وَ بَلِّغْنَا رَمَضَان
"Allahumma barik lana fi Rajab wa Sha'ban wa ballighna Ramadan"...
Meaning: O Allah! Make the months of Rajab and Sha'ban blessed for us, and let us reach the
month of Ramadan (i.e. prolong our life up to Ramadan, so that we may benefit from its merits and blessings)
[Narrated by at-Tabarani and Ahmad]