Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him) that he (peace and blessings be upon him) said: "Allah, the Mighty and Majestic, looks upon His creation on the night of the middle of Sha'ban, and forgives all His creation except a polytheist or one who harbours enmity."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17351