Shaykh al-Albaanee rahimahullaah mentions in his ‘Silsilatul-Ahaadeeth as-Saheehah‘ vol. 3 pp. 135:
((Allaah the Exalted and Most High looks down at His creation the night of the middle of Sha`baan, so he forgives all of His creation, except for a polytheist [mushrik] or one who has enmity [in his heart].))
He said: “[This is] an authentic narration, reported from a group of the Companions with different chains of narrations that strengthen each other. And they are: Mu`aadh bin Jabal, and Abu Tha`labah al-Khushanee, and Abdullaah bin `Amr, and Abu Moosaa al-Ash`aree, and Abu Hurayrah, and Abu Bakr as-Siddeeq, and `Awf bin Maalik, and `Aaishah [may Allaah be pleased with them all].
Reported by Ibn Abee `Aasim in ‘as-Sunnah‘ no. 512…”
 Sha`baan: the eighth month of the Islamic calendar, the month preceding Ramadaan.