Very early Hadith books such as the Mussanaf of Abdul Razzaq Ibn Humam
(May Allaah have mercy on him) (126-211 AH)( Ref: Musannaf Abdur Razzaq 4/317) and the Musnad of Ahmed bin Hanbal (May Allaah have mercy on him) (164-241 AH) ( Ref: Musnad Ahmad 2/176 & 6/238)contain Ahadith relating to the virtues of 15th Sha'ban.
Even within the famous Six Books of Hadith (al-Kutub al-Sittah), Trimdhi ( Ref: Jami' Al-Trimidhi: Kitab Al-Sawm, Bab "Ma ja'a fi Laylatin Nisfi min Sha.ban" #739 (Vol.3 p107))and Ibn Majah (Sunan Ibn Majah: Kitab Al-Iqamah, Bab "Ma Ja'a Fi Laylatun Nifsi min Sha'ban" #1388 (Vol. 1 p444) have devoted a special chapter on "The Night of the Middle of Sha'ban" in their Hadith collections. In fact there are over a dozen Ahadith available which establish the significance of the night of the 15th of Sha'ban.
There are many hadith on the merits of this Night and some of them are weak ( dai’f).However, it is to be noted that not all of the 'weak' Ahadith suffer from major weaknesses and in fact the minor weaknesses in some Ahadith are curable and strengthened by other narrations.
( Wahabi Scholar Albani : : Silsilah Al-Ahadith Al Sahihah 3/135)
When all the numerous weak Ahadith are combined together, they reach a level of acceptability among Hadith scholars equivalent to being 'Hasan' (good).
Here are a few Sahih (Authentic) Hadith on the merits on the Night of 15 th of Shaba’an.
Ibn Hibban narrated from Mu`adh ibn Jabal in his Sahih the following narration which the hadith scholar and editor of the Sahih Shu`ayb Arna'ut confirmed as sound:
The Prophet said : yattali`u Allahu ila khalqihi fi laylati al-nisfi min sha`bana fa-yaghfiru li-jami`i khalqihi illa li mushrikin aw mushahin.
Allah looks at His creation in the night of mid-Sha`ban and He forgives all His creation except for a mushrik (idolater) or a mushahin (one bent on hatred).
( Reference: Al-Tabarani: Al-Mu'jam Al-Kabir 20/108-9, Ibn Hibban:
Sahih Ibn Hibban 7/470, Al-Bayhaqi: Shu'bal Iman 2/288, Abulhasan
Al-Qazwini: Al-Amali 4/2, Ibn 'Asakir: Al-Tarikh 15/302 & Ibn Abi 'Asim:Al-Sunna1/224)
1)Ibn Hibban (May Allaah have mercy on him) considered this Hadith to be Sahih.
(Ibn Rajab: Lataif Al-Ma'arif 1/224)
2)And Ibn Hajr Al-Haytami (May Allaah have mercy on him) said: "This Hadith is related by Al-Tabarani (May Allaah have mercy on him) in Al-Mu'jam Al-Kabir and Al-Awsat and the narrators of both are trustworthy"(thiqat) ( Ibn Hajar Al-Haytami: Majma' Al-Zawaid 8/65)
3)The great hadith scholar of the present time , Shaykah Shuayb Al-Arna'uat ( Rh) and the self claimed Wahabi hadith scholar Nasiruddin Al-Albani, have also considered this Hadith as 'Sahih'.
( Ref: - Shuayb Al-Arna'ut: Al-Ihsan fi Taqrib Sahih Ibn Hibban 12/481 #5665 & Nasiruddin Al-Albani: Silsilah Al-Ahadith Al-Sahihah 3/135 #1144 )
There is another identical Hadith related from the Companion Abdullah b.'Amr (May Allaah be pleased with him) which says that the Prophet(Sallalahu Alaihi Wassalam) said: "Allah looks at His creation during the night of the 15th of Sha'ban and He forgives His servants except two- one intent on hatred (mushanin) and a murderer (qatilu nafs).
( Ref : Musnad Ahmad 2/176 #6642. Al-Bazzar also related this Hadith and he classified it as 'hasan'. )
In his edition of Musnad Ahmed, Shaykh Ahmed Shakir has classified this Hadith as'Sahih' and Nasiruddin Al-Albany classified it is 'Hasan'
( Al-Albani: Silsilah Al-Ahadith Al-Sahihah 3/136).
A similar narration as above , but narrated by Abu Bakr Siddiq Rd .
It has been classified as sound by Haafiz al-Munzhiri (RA) in his al-Targheeb (vol.3 pg.459). This narration is of Sayyiduna Abu Bakr (Radhiallaahu Anhu) and is recorded by Imaam Bazzaar (RA) in his Musnad. In fact, Hafiz ibn Hajar (RA) has also classified one of its chains as Hasan (sound). (al-Amaalil mutlaqah pgs.119-120)
An important Note:
All the weak hadith which talks about the merits of 15th of Shaba’an, have got only minor weakness in them. Going by the principle of hadith, these weak hadiths also strengthen each other.
Besides the above, there are many other Sahaaba (Radhiallaahu Anhum) that narrated Ahaadith regarding the merit of this night, such as: Abu Hurayra (Musnad al-Bazzaar), Abu Tha’labah (Shu’ubul Imaan), Awf ibn Maalik (Musnad al-Bazzaar), Abdullah ibn Amr ibn al-Aas (Musnad Ahmad Hadith6642), Abu Moosa al-Ash’ari (ibn Majah Hadith1390; Shu’ubul Imaan Hadith3833) and others. The collective strength of these narrations cannot be refuted.
What the Scholars have said about this Night:
1) The general virtue of this night has been accepted by many great Ulama of the past. From among many great scholars which have agreed to the virtue of this night are: Umar ibn Abdul-Aziz, Imaam al-Shaafi’ee, Imaam al-Awzaa’ie, Attaa ibn Yassaar, Imaam al-Majd ibn Taymiyah, ibn Rajab al-Hambaliy and Hafiz Zaynu-ddeen al-Iraaqiy (Rahmatullaahi alayhim) .
Refer Lataiful Ma’aarif of Hafiz ibn Rajab pgs.263-264 and Faydhul Qadeer vol.2 pg.317.
2) Even Ibn Taymiyya -- the putative authority of "Salafis" -- considered the night of mid-Sha`ban "a night of superior merit" in his Iqtida' al-sirat al-mustaqim:
[Some] said: There is no difference between this night (mid-Sha`ban) and other nights of the year. However, the opinion of many of the people of learning, and that of the majority of our companions (i.e. the Hanbali school) and other than them is that it is a night of superior merit, and this is what is indicated by the words of Ahmad (ibn Hanbal), in view of the many ahadith which are transmitted concerning it, and in view of what confirms this from the words and deeds transmitted from the early generations (al-athar al-salafiyya). Some of its merits have been narrated in the books of hadith of the musnad and sunan types. This holds true even if other things have been forged concerning it.
( Ref:Ibn Taymiyya, Iqtida' al-sirat al-mustaqim (1369/1950 ed.) p. 302.)
Ibn Taymiayh also said
“ As for the middle night of Sha’baan, there are various narrations that have been narrated regarding its significance and it has been reported from a group of the Salaf (predecessors) that they performed Salaat in it individually, hence, such a deed cannot be disputed.’
(Majmoo’ al-Fataawa ibn Taymiyah vol.23 pg.132)
3) Imam Suyuti (Rh)says in his Haqiqat al-sunna wa al-bid`a:
“As for the night of mid-Sha`ban, it has great merit and it is desirable (mustahabb) to spend part of it in supererogatory worship.”
( Ref: Suyuti, Haqiqat al-sunna wa al-bid`a aw al-amr bi al-ittiba` wa al-nahi `an al-ibtida` (1405/1985 ed.) p. 58. He adds: "However, this must be done alone, not in congregation.")
4. Imam Haskafi ( Rh) said in his Durr al-Mukhtar, one of the primary references in the Hanafi school:
"Among the recommended [prayers] are on. . . . the nights of the two Eids, the middle of Sha`ban, the last ten of Ramadan, and the first [ten] of Dhul-Hijjah”.
5. Imam Nawawi ( Rh) mentioned in his Majmu`, where he also quoted Imam al-Shafi`i from the latter’s al-Umm that it has reached him that there are 5 nights when dua is answered, one of them being the night of the 15th of Sha`ban.
Only Sahih hadiths have been quoted above. The weak hadith on this topic suffer only from minor weakness . There is general consensus that weak hadiths may be acted upon for virtuous acts, such as voluntary fasting and prayer, as long as the hadith is not excessively weak, returns to a general basis in the Shariah, and one is not convinced that the Prophet (Allah bless him & give him peace) specifically prescribed it.
There are many other narrations from the Companions and early Muslims confirming the merits of this night as mentioned by Ibn Rajab al-Hanbali in his Lata’if al-Ma`arif, and others.