Question Summary:
Did the Sahabah prepare for Ramadan six months in advance?

Question Detail:

Is it true and is it stated in hadith that sahabah used to prepare for ramadhan month 6 month before?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh. 
The statement in reference is not a Hadith.
However, it is mentioned in Lata`if al-Ma`arif (p. 280, Dar Ibn Kathir, Damascus/ Beirut) by Imam Ibn Rajab al-Hanbali (736-795 A.H):
قال مُعلّى بن الفضل: كانوا يدعون الله تعالى ستة أشهر أن يبلّغهم رمضان، ثم يدعونه ستة أشهر أن يتقبله منهم. وقال يحيى بن أبي كثير: كان من دعائهم: اللهم سلِّمني إلى رمضان، اللهم سلم لي رمضان، وتَسلَّمه منّي متقبَّلا.
Translation: Mu`alla bin al-Fadhl states: They (the sahabah) would supplicate to Allah Ta`ala for six months to allow them to reach Ramadhan. Then, they would supplicate to Him another six months to accept it from them. Yahya bin Abi Kathir states: it was from their supplication:
اللهم سلِّمني إلى رمضان، اللهم سلم لي رمضان، وتَسلَّمه منّي متقبَّلا
Transliteration: Allahumma sallimnee ilaa Ramadhan, Allahumma sallim lee Ramadhan, wa tasallamhu minnee mutaqabbalaa
Translation: O Allah, commit me to Ramadan. Oh Allah commit Ramadan for me. And receive it from me with acceptance.
And Allah Ta’āla Knows Best
Hanif Yusuf Patel
Student Darul Iftaa
UK
Checked and Approved by,
Mufti Ebrahim Desai.
www.daruliftaa.net