Translation: The Messenger of Allah ﷺ said:
665. Narrated Abu-Huraira: " The Prophet said: " None of you should observe fasting for a day or two ahead of Ramadhan, unless he has the habit of observing fasting and if his voluntary fasting coincides with that day, then he can observe fasting that day. " (Bukhari)
Translation: 666. Narrated Abu-Huraira; ' The Prophet or Abul- Qasim said: " Start fasting on seeing the crescent (of Ramadhan), and give up fasting on seeing the crescent (of Shawwal), and if it is overcast (and you cannot see the crescent), complete thirty days of Sha'aban. " (Bukhari)
Translation: 667. Narrated Abu-Huraira: ' The Messenger of Allah ﷺ said: “ If the last half of Sha'aban remained, do not observe fasting. " " " (At-Termizi)
Translation: Abu-Issa said: " The meaning of this Hadith to some people of knowledge is that a man who does not observe fasting during the first days of Sha'aban, and when some days of it remain, he starts to observe fasting. In other words, he did not observe fasting during the first half of the month and when there were only few days of it remains, he starts to observe fasting. Such a form of voluntary fasting is undesirable. "
Translation: 668. Narrated Silah ibn Zofar: ' We were with Ammar ibn Yasir and a roasted sheep was brought to him. He said to the attendees: " Eat. " Some of them refused to eat saying: " I am observing fasting. " A mar said: " He that observes fasting on Yawm Al-Shakk23, has disobeyed Abul-Qasim. " " "
Abu-Issa said: " The Hadith of Ammar is Hasan Saheeh and the people of knowledge from the Prophet's companions and the successors acted upon it. They disliked that a man observed fasting on the day that the people have doubt about it. Most of them said: ' If a man observed fasting on that day and it came clear later that it was of the month of Ramadhan, he should repeat it. 511 "
Translation: 23 Yawm Al-Shakk (the doubted day) is the thirtieth day of Sha'aban, if the new moon was not seen due to clouds or other reasons. Thus, it is likely that it is either the final day of Sha'aban or the first day of Ramadhan.