Sunan Ibn Majah, Volume 2, Book 7, Hadith 1647 (DarusSalam) ⓘ

It was narrated from Qasim Abu ‘Abdur-Rahman that he heard Mu’awiyah bin Abu Sufyan on the pulpit saying: “The Messenger of Allah used to say from the pulpit, before the month of Ramadan: ‘Fasting will begin on such and such a day, but we are going to start fasting earlier, so whoever wants to start fasting earlier (i.e., in Sha’ban), let him do so, and whoever wants to wait until Ramadan begins, let him do so.’”

حَدَّثَنَا الْعَبَّاسُ بْنُ الْوَلِيدِ الدِّمَشْقِيُّ، حَدَّثَنَا مَرْوَانُ بْنُ مُحَمَّدٍ، حَدَّثَنَا الْهَيْثَمُ بْنُ حُمَيْدٍ، حَدَّثَنَا الْعَلاَءُ بْنُ الْحَارِثِ، عَنِ الْقَاسِمِ أَبِي عَبْدِ الرَّحْمَنِ، أَنَّهُ سَمِعَ مُعَاوِيَةَ بْنَ أَبِي سُفْيَانَ، عَلَى الْمِنْبَرِ يَقُولُ كَانَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ يَقُولُ عَلَى الْمِنْبَرِ قَبْلَ شَهْرِ رَمَضَانَ ‏ "‏ الصِّيَامُ يَوْمَ كَذَا وَكَذَا وَنَحْنُ مُتَقَدِّمُونَ فَمَنْ شَاءَ فَلْيَتَقَدَّمْ وَمَنْ شَاءَ فَلْيَتَأَخَّرْ ‏" ‏ ‏.‏