The most beloved month for the Messenger of Allah ﷺ to fast was Shaban, which he would then connect with Ramadan.
كان أحب الشهور إلى رسول الله ﷺ أن يصومه شعبان، ثم يصله برمضان.
Abu Dawud (2431) narrated it from Ahmad, and it is in his Musnad (25548), and Nasai (2350), and Ibn Khuzayma (2077) and Hakim (1/434) graded it sahih. All of them narrated it through Muawiya bin Salih, from Abdullah bin Abu Qays, who heard Ayesha say it, as mentioned. Its isnad is hasan because of Muawiya bin Salih, for his hadith is hasan.