Is it Sunnah to recite اللهم بارك لنا في رجب وشعبان وبلغنا رمضان after every Ṣalāh in Rajab?
بسم الله الرحمن الرحیمAnswer
Anas ibn Mālik (d. 93/711-2) (may Allah be pleased with him) says that when the month of Rajab would commence, the Prophet ﷺ would say: اللهم بارك لنا في رجب وشعبان وبلغنا رمضان (O Allah, bless us in Rajab and Shaʿbān and allow us to reach Ramaḍān). There is a difference of opinion regarding the status and authenticity of this narration. According to Imam Nawawī (d. 676/1277), Ḥafiẓ Ibn Rajab (d. 795/1393), ʿAllāmah Ṭāhir Pattanī (d. 986/1578-9) and Mawlānā ʿAbd al-Ḥayy Laknawī (d. 1304/1886), it is permissible to act upon this narration despite its weakness.
The ḥadīth suggests that the duʿāʾ should be read when the month commences and makes no reference to reading this duʿāʾ after each Ṣalāh.
My respected father Shaykh al-Ḥadīth Mufti Shabbir Ahmad (b. 1376/1957 – ) was once asked regarding this. He advised that one should read the masnūn duʿās and adhkār after Ṣalāh that have been narrated from the Prophet ﷺ. He further mentioned that the ḥadīth states that the Prophet ﷺ would recite the duʿāʾ when the month of Rajab would commence. This is similar to the duʿāʾ which the Prophet ﷺ would read upon sighting the moon each month. The narrations do not suggest that the Prophet ﷺ would continue to read the duʿāʾ of sighting the moon throughout the month. There are duʿās for different occasions and the Rajab duʿāʾ was read upon the commencement of the month. Whilst it is permissible to seek the blessings of Allah and supplicate with this duʿāʾ throughout Rajab like any other duʿāʾ, one should not regard this as the practice of the Prophet ﷺ.
Allah knows best
1 Rajab 1436 / 20 April 2015
 This narration has been narrated in Musnad Aḥmad (2346), ʿAmal al-Yawm Wa al-Laylah (659), Shuʿab al-Īmān (3534), Ḥilyah al-Awliyāʾ (6: 269), Musnad al-Bazzār (6496), al-Duʿāʾ (911), al-Muʿjam al-Awsaṭ (3939), Tārīkh Baghdad (16: 85), Tārīkh Dimashq (40: 57) and others books. The chains of all these narrations have two main defects. Firstly, the presence of Zāʾidah ibn Abī al-Raqād (n.d.), a weak narrator who relates munkar (unknown) narrations from Ziyād al-Numayrī (n.d.). (See al-Tārīkh al-Kabīr, 3: 433; Mīzān al-Iʿtidāl, 2: 65; Shuʿab al-Īmān, 3534; al-Jarḥ Wa al-Taʿdīl, 3: 613; al-Majrūḥīn, 1: 308; Tahdhīb al-Kamāl, 9: 272; Tahdhīb al-Tahdhīb, 3: 305). However, some scholars have deemed him acceptable to an extent. (See al-Jarḥ Wa al-Taʿdīl, 3: 613; al-Kāmil, 4: 196; Majmaʿ al-Zawāʾid, 3: 140; Tārīkh Baghdad, 2: 401; Tahdhīb al-Kamāl, 9: 272). Secondly, the presence of Ziyād ibn ʿAbd Allah al-Numayrī (n.d.), a weak narrator according to many experts though some have deemed him acceptable. (See Mīzān al-Iʿtidāl, 2: 65; al-Jarḥ Wa al-Taʿdīl, 3: 536; Tahdhīb al-Kamāl, 9: 492; Tahdhīb al-Tahdhīb, 3: 378).
Accordingly, scholars have differed whether this ḥadīth regarding Rajab should be acted upon. Shaykh Ṭāhir Pattanī (d. 986/1578-9) is of the view that the narration is weak, not unfounded, and that it is permissible to act upon weak narrations in matters of virtue (Tadhkirah al-Mawḍūʿāt, p. 117). This also appears to be the view of Imam Tabrīzī (d. ca. 741/1340) (Mishkāt al-Maṣābīḥ, 1369), Imam Nawawī (d. 676/1277) (al-Adhkār, p. 189), Ḥāfiẓ Ibn Rajab al-Ḥanbalī (d. 795/1393) (Laṭāʾif, p. 172; Sharḥ al-Zurqānī ʿAlā al-Mawāhib, 10: 480) and Mawlānā ʿAbd al-Ḥayy Laknawī (d. 1304/1886) (al-Āthār al-Marfūʿah, 1: 59). ʿAllāmah Haythamī (d. 807/1405) also seems inclined to this (Majmaʿ al-Zawāʾid, 3: 140) although in another place he seems inclined to the view that Ziyād is munkar al-ḥadīth (Ibid, 2: 165). This is in line with the view of other scholars who have deemed this narration unacceptable to use because it is singularly transmitted by Ziyād who is munkar al-ḥadīth in his narrations from Ziyād. This appears to be the view of Imam Bukhārī (d. 256/870), Shaykh al-Islām Ibn Taymiyah (d. 728/1328) (Majmūʿ al-Fatāwā, 25: 291) and Ḥāfiẓ Dhahabī (d. 748/1348) (al-Mugnī, 1: 236). Imam Bayhaqī (d. 458/1066) and ʿAllāmah Munāwī (d. 1031/1622) (Fayḍ al-Qadīr, 5: 131) also appear to be inclined towards this. It is worth noting that when Imam Bukhārī describes a narrator as munkar al-ḥadīth, it is not permissible to transmit from him according to him (Ṭabaqāt al-Shāfiʿiyyah al-Kubrā, 2: 224). Ḥāfiẓ Ibn Ḥajar al-ʿAsqalānī (d. 852/1449) is of the view that the narration is weak, not fabricated (Tabyīn al-ʿAjab bimā Warada fī Shahr Rajab, p. 37). However, it is not entirely clear whether it can be practiced upon according to him or not. He has further highlighted a chain for this narration which on the face of it appears to be ṣaḥīḥ (sound), however, it is fabricated.
Based on the above, there is no harm in reading this supplication as a group of scholars have deemed it acceptable. However, it should not be overemphasised or regarded as a sound (ṣaḥīḥ) narration or attributed directly with certainty to the Prophet ﷺ.
 Sunan al-Tirmidhī (3451); Muṣannaf ʿAbd al-Razzāq (7350); Muṣannaf Ibn Abī Shaybah (2: 343); Musnad Aḥmad (1397); Sunan al-Dārimī (1729); Musnad al-Bazzār (947); Ṣaḥīḥ Ibn Ḥibbān (888); al-Mustadrak (7767); ʿAmal al-Yawm Wa al-Laylah (641).