In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
We do not know of anything in the religious texts to indicate that it is recommended to have sex with one’s wife on Friday night.
Answering your question, the Fatwa Center at Islam Q and A, states:
We do not know of anything in the Islamic texts to indicate that it is recommended for a man to have sex with his wife on Friday night [i.e., the night before Friday] in particular, let alone that he will have a double reward for doing that.
But some of the scholars are of the view that it is recommended to have intercourse with one’s wife on Friday, because the Prophet (peace be upon him) said: “Whoever does ghusl from janabah on Friday, then comes to the mosque early, it is as if he sacrificed a camel…” (Al-Bukhari and Muslim)
An-Nawawi (may Allah have mercy on him) said:
“The words of the Prophet (peace be upon him), “Whoever does ghusl from janabah on Friday” refer to ghusl that resembles the ghusl from janabah in the way it is done [as the Arabic text may be understood in that way]. This is the well-known view concerning the interpretation of this report.
Some of our companions said in the books of fiqh: What is meant is ghusl from janabah in a real sense. They said: It is recommended for him to have intercourse with his wife, because that is more effective in helping him to lower his gaze and to have a sense of calm and ease.
But this view is weak or false, and the correct view is what we have mentioned above.” (Sharh An-Nawawi ala Muslim, 6:135)
Al-Hafizh Ibn Hajar (may Allah have mercy on him) said:
“According to a report narrated by Ibn Jurayj from Sumayy, that was recorded by ‘Abd ar-Razzaq: “… and one of you does ghusl as he does from janabah…” What appears to be the case is that the resemblance is in the way it is done, not in the ruling. This is the view of the majority.
And it was said that this indicates that one may have intercourse on Friday so that he might do ghusl from janabah on that day. And the wisdom behind it is so that he might have a sense of calm and ease when going to the prayer, and will be less likely to let his gaze wander. This also causes the woman to do ghusl on that day.
An-Nawawi said: Some of our companions were of this view, but it is weak or false, and the correct view is the first one.
Ibn Qudamah narrated this view from Imam Ahmad, and also proved it to be soundly narrated from a number of the tabi`een.
Al-Qurtubi said that it is the most likely view to be correct, so there is no way to claim that it is invalid, even if the first view is more likely to be correct. Perhaps he meant that it is invalid according to his madhhab.” (Fath al-Bari, 2:366)
They also quoted as evidence the words of the Prophet (peace be upon him): “Whoever does ghusl and causes his wife to do ghusl, comes early to the mosque, sits close to the imam and does not engage in idle talk, will have for every step he takes the reward of one year, its fasting and prayer.” (Abu Dawud, At-Tirmidhi and An-Nasa’i)
An-Nawawi (may Allah have mercy on him) noted that there are two versions of the hadith, which use different forms of the verb ghasala (wash), namely ghasala (to wash) and ghassala (to make someone else wash).
If we accept the report which says ghassala (make someone else wash), then it may be understood in the following three ways:
1- That he causes his wife to do ghusl by having intercourse with her, which means that she has to do ghusl, and he will do ghusl too. They said: It is recommended for him to have intercourse on this day, so as to protect him from seeing anything on his way (to the mosque) that could distract him.
2- That what is meant is washing the limbs when doing wudu, washing each one three times, then doing ghusl for Friday Prayer.
3- Washing his garment and his head, then doing ghusl for Friday Prayer.
If we accept the report which says ghasala (wash), then it may be understood in the following three ways:
1- That it refers to intercourse, as was stated by al-Azhari, who said: It may be said of a man ghasala imra’atahu, if he has intercourse with her.
2- That it refers to his washing his head and his garment.
3- That it refers to wudu.
The preferred view is that which was preferred by Al-Bayhaqi and other scholars, which is that the word is ghasala and refers to washing the head.
This is supported by a version of this hadith which was narrated by Abu Dawud: “Whoever washes his head on Friday and does ghusl.”
Abu Dawud in his Sunan and Al-Bayhaqi narrated this interpretation from Makhul and Sa‘eed ibn ‘Abd al-‘Azeez.
“It is explained in the report of Abu Dawud and Ibn ‘Abbas (may Allah be pleased with them) from the Prophet (peace be upon him).
The head is singled out for mention because they used to put oil and marsh mallow (Althaea officinalis) and the like on their heads [to clean the hair], and they used to wash the head first, then do ghusl.” (Al-Majmu‘ Sharh al-Muhadhdhab, 4:543)
What is most likely to be correct is that the hadiths which speak of the instruction to do ghusl on Fridays have to do with going to Friday prayer, because it is recommended to do ghusl and put on perfume to go to the prayer, and none of them have anything to do with it being recommended to do have sex on this day.
Almighty Allah knows best.