Hadith #39
Arabic Text
وَبِإِسْنَادِهِ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ لَا تَقَدَّمُوا الشَّهْرَ بِيَوْمٍ وَلَا يَوْمَيْنِ إِلَّا أَنْ يُوَافِقَ أَحَدُكُمْ صَوْمًا كَانَ يَصُومُهُ صُومُوا لِرُؤْيَتِهِ وَأَفْطِرُوا لِرُؤْيَتِهِ فَإِنْ غُمَّ عَلَيْكُمْ فَأَتِمُّوا ثَلَاثِينَ يَوْمًا ثُمَّ أَفْطِرُوا
English Translation
And with the same chain of narration, the Messenger of Allah ﷺ said: 'Do not precede the month by a day or two, unless it coincides with a fast that one of you regularly observes. Fast upon sighting it (the crescent moon) and break the fast upon sighting it. If it is obscured from you, then complete thirty days, then break the fast.'
Quran References
Reference: Musnad Ahmad, Book 21, Hadith 39
Sunnah.com ref: Musnad Ahmad 9277
Islam.wiki ID: IWH-45667