Praise be to Allah.
It was proven in al-Saheehayn in the hadeeth of Abu Hurayrah (may Allaah be pleased with him) that he said: “I heard the Prophet (peace and blessings of Allaah be upon him) say, ‘None of you should fast on a Friday unless he fasts the day before or the day after.’” (Narrated by al-Bukhaari, 1849, Muslim, 1929). Muslim narrated in his Saheeh that the Prophet (peace and blessings of Allaah be upon him) said, “Do not single out the night of Jumu’ah [i.e., Thursday night] from among other nights for praying qiyaam al-layl, and do not single out Friday from among other days for fasting, unless it is a fast that one of you regularly observes.” (al-Siyaam, 1930)
In al-Saheeh it was narrated from Juwayriyah bint al-Haarith (may Allaah be pleased with her) that the Prophet (peace and blessings of Allaah be upon him) entered upon her on a Friday when she was fasting. He asked her, “Did you fast yesterday?” She said, “No.” He asked, “Are you going to fast tomorrow?” She said, “No.” He said, “Then break your fast.” Hammaad ibn al-Ja’d said, “I heard Qutaadah say, Abu Ayyoob told me that Juwayriyah spoke to him and he told her to stop her fast and she did so.” (Narrated by al-Bukhaari, al-Sawm, 1850).
Ibn Qudaamah said: “It is makrooh to single out the day of Friday for fasting, unless that coincides with a fast which one usually observes, such as a person who fasts alternate days, and a day that he fasts coincides with Friday, or a person who has the habit of fasting on the first or last day of the month, or the middle day of the month.” (al-Mughni, vol. 3, p. 53)
Al-Nawawi said: “Our companions (i.e. the Shaafa’is) said: it is makrooh to single out the day of Friday for fasting, but if one joins it with the day before or the day after, or it coincides with a day which he habitually fasts, or he vowed to fast the day that his sick loved one was cured, or the day So and so returns, and that day happens to be a Friday, then it is not makrooh (al-Majmoo’ Sharh al-Muhadhdhab, vol. 6, p. 479)
Shaykh al-Islam (may Allaah have mercy on him) said: “The Sunnah says that it is makrooh to single out Rajab for fasting, and it is makrooh to single out Friday (for fasting).” (al-Fataawa al-Kubra, vol. 6, p. 180)
Shaykh Ibn ‘Uthaymeen said: “As for Friday, it is not Sunnah to fast on this day, and it is makrooh to single it out for fasting.” (See al-Sharh al-Mumti’, vol. 6, p. 465)
Excluded from this prohibition is one who fasts the day before or after, or if it coincides with days that he habitually fasts, such as one who fasts al-Ayyaam al-Beed (the 13th, 14th and 15th of each hijri month), or who has the habit of fasting a specific day such as the Day of ‘Arafat, and it coincides with a Friday. From this it may be understood that it is permissible for a person who has vowed to fast on the day when So and so returns, for example, or the day when So and so recovers from sickness, to observe that fast if that day happens to be a Friday. (See Fath al-Baari by Ibn Hajar).
The same applies to one who has fasts to make up from Ramadaan. “It is permissible for a Muslim to fast on a Friday to make up a day from Ramadaan, even if he fasts the Friday on its own.” (Fatwa al-Lajnah al-Daa’imah, vol. 10, p. 347)
Similarly, if ‘Ashoora’ or Arafaat coincides with a Friday, he may fast, because his intention is to fast ‘Ashoora’ or ‘Arafaat, not to fast on a Friday. And Allaah is the Source of strength.