عَنْ أَبِي هُرَيْرَةَ رضى الله عنه
قَالَ: قَالَ رَسُولُ اَللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ -«لَا تَقَدَّمُوا رَمَضَانَ بِصَوْمِ يَوْمٍ وَلَا يَوْمَيْنِ، إِلَّا رَجُلٌ كَانَ يَصُومُ صَوْمًا، فَلْيَصُمْهُ»
“None of you should fast a day or two before the (beginning of the) mouth of Ramadan, unless it is a day on which one is in the habit of fasting (i.e. voluntary fasting that coincides with that day).” Agreed upon.
Bulugh al-Maram 758, Book 5, Fasting, Hadith 1. 1 min read