رياض الصالحينAbū Zakariyyā Muḥyī al-Dīn Yaḥyā ibn Sharaf al-Nawawī٢١٩ - باب النهي عن تقدم رمضان بصوم بعد نصف شعبان إلا لمن وصله بما قبله أو وافق عادة له بأن كان عادته صوم الإثنين والخميس فوافقه
On the authority of Abū Hurayrah (may Allah be pleased with him), from the Prophet (peace and blessings be upon him), who said: "Let none of you anticipate Ramadan by fasting a day or two beforehand, unless it be a man who was already in the habit of keeping such a fast, in which case let him fast that day." Agreed upon (al-Bukhārī and Muslim).
On the authority of Ibn ʿAbbās (may Allah be pleased with them both), who said: The Messenger of Allah (peace and blessings be upon him) said: "Do not fast before Ramadan; fast at the sighting of it and break your fast at the sighting of it. If a cloud obscures it from you, then complete thirty days." Narrated by al-Tirmidhī, who said: "a good (ḥasan), sound (ṣaḥīḥ) hadith." The word "al-ghayāyah" is spelt with the dotted ghayn and with the doubled yāʾ that is dotted below, and it means: the cloud.
On the authority of Abū Hurayrah (may Allah be pleased with him), who said: The Messenger of Allah (peace and blessings be upon him) said: "When half of Shaʿbān remains, do not fast." Narrated by al-Tirmidhī, who said: "a good (ḥasan), sound (ṣaḥīḥ) hadith."
On the authority of Abū al-Yaqẓān ʿAmmār ibn Yāsir (may Allah be pleased with them both), who said: Whoever fasts the day about which there is doubt has disobeyed Abū al-Qāsim (peace and blessings be upon him). Narrated by Abū Dāwūd and al-Tirmidhī, who said: "a good (ḥasan), sound (ṣaḥīḥ) hadith."