Abu Hurairah (RAA) narrated that The Messenger of Allah (ﷺ) said:
"When it is the middle of Sha'ban do not fast (until it is Ramadan)." Related by the five Imams, but Imam Ahmad declared it to be a weak narration. (ID)
English reference (ID): Book 5, Hadith 711 (ID)
Arabic reference (ID): Book 5, Hadith 691 (ID)