The month most liked by the Messenger of Allah (ﷺ) for fasting was Sha'ban. He then joined it with Ramadan.
Sunan Abi Dawud Book 14, Hadith 119
← Previous Hadith I asked Sa'id b. Jubair about fasting during Rajab. He said: Ibn 'Abbas told me that the Messenger of Allah (ﷺ) used to fast to such an extent that we thought that he would never break his fast; and he would go without fasting to such an extent that we thought he would never fast.

Sunan Abi Dawud Book 14, Hadith 118 Next Hadith → I asked or someone asked the Prophet (ﷺ) about perpetual fasting. He replied: You have a duty to your family. Fast during Ramadan and the following month, and every Wednesday and Thursday. You will then have observed a perpetual fast.

Sunan Abi Dawud Book 14, Hadith 120