Ruling on fasting seven consecutive days voluntarily
Question

Is it permissible to fast for an entire week apart from the obligatory month, with the intention of fasting voluntarily, starting on Saturday and ending on Friday?
Praise be to Allah.It is permissible for a person to fast voluntarily for seven days or ten days one after another, because of the hadeeth of ‘Aa’ishah (may Allah be pleased with her) who said: The Messenger of Allah (blessings and peace of Allah be upon him) used to fast until we would say, he will never stop fasting, and he used not to fast until we would say, he will never fast. I never saw the Messenger of Allah (blessings and peace of Allah be upon him) fast any entire month except Ramadan, and I never saw him fast more than he did in Sha‘baan.
Narrated by al-Bukhaari (1833) and Muslim (1956).
According to a report narrated by Abu Dawood (2313), from Umm Salamah, from the Prophet (blessings and peace of Allah be upon him): He never fasted a complete month in the year except Sha‘baan, and he would join Ramadan to it.
Classed as saheeh by Shaykh al-Albaani in Saheeh Abi Dawood.
It was also narrated from her that Hamzah ibn ‘Amr al-Aslami asked the Messenger of Allah (blessings and peace of Allah be upon him): O Messenger of Allah, I am a man who fasts several days in a row; can I fast when travelling? He said: “Fast if you wish and do not fast if you wish.”
Narrated by Muslim, 1890.
Based on that, it is permissible to fast continuously for several days of the month in a row; that is not included in the fasting that is forbidden, namely fasting all the time.
We have previously discussed the ruling on fasting all the time in the answer to question no. 144592
Shaykh Ibn Jibreen (may Allah have mercy on him) was asked: What is the ruling on fasting every day, one after another, because of special circumstances, based on one interpretation of the hadeeth which says: The Messenger of Allah (blessings and peace of Allah be upon him) used to fast until we would say, he will never stop fasting, and he used not to fast until we would say, he will never fast? How sound is it to quote this hadeeth as evidence?
He replied: It is permissible to fast several days in a row, then to not fast for several days in a row. The evidence for that is the hadeeth mentioned in the question, because that is voluntary and is mustahabb.
End quote from Fataawa Ibn Jibreen
And Allah knows best.