Virtue of fasting in Rajab

An uncle told me that “… if you fast in rajab Allah Ta'ala on the day of judgment will give you a drink from His own hands from the river of Rajab which is whiter than milk sweeter than honey…”

I did some research and didn’t find any Hadith claiming this and I found out that there isn’t any evidence to back there being a specific reward for fasting during Rajab. I didn’t respond to his text to avoid trouble. My family is South Asian and bidah/cultural practices are rife.