Is the hadith “Rajab is the month of seeking forgiveness for my Ummah” authentic?

What has been mentioned regarding increasing istighfar (seeking forgiveness) in Rajab—we have not found it to be an authentic hadith. However, a weak hadith has been narrated with the wording: "Increase istighfar in the month of Rajab, for Allah has in every hour of it those freed from the Fire, and Allah has cities that none shall enter except one who fasts Rajab." This hadith is very weak, as al-Asbagh, who is in its chain of narration, "is nothing." Nevertheless, it is recommended for a Muslim to increase istighfar in all months.