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Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
tirmidhi:937 – Aḥmad b. Manīʿ > al-Ḥasan b. Mūsá > Shaybān > Manṣūr > Mujāhid > Ibn ʿUmar

"The Prophet performed Umrah four times, one of them was during Rajab."  

Abū ʿĪsá said that this Ḥadīth is Ḥasan-Ṣaḥīḥ-Gharīb.
الترمذي:٩٣٧ – حَدَّثَنَا أَحْمَدُ بْنُ مَنِيعٍ حَدَّثَنَا الْحَسَنُ بْنُ مُوسَى حَدَّثَنَا شَيْبَانُ عَنْ مَنْصُورٍ عَنْ مُجَاهِدٍ عَنِ ابْنِ عُمَرَ

أَنَّ النَّبِيَّ ﷺ اعْتَمَرَ أَرْبَعًا إِحْدَاهُنَّ فِي رَجَبٍ  

قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ غَرِيبٌ

See similar narrations below:

Collected by Ṭabarānī
tabarani:13523 – [Chain 1] Ibrāhīm b. Aḥmad al-Wakīʿī from my father [Chain 2] Aḥmad b. Shuʿayb Abū ʿAbd al-Raḥman al-Nasāʾī > Muḥammad b. Rāfiʿ al-Naysābūrī > Yaḥyá b. Ādam > Mufaḍḍal b. Muhalhal > Manṣūr > Mujāhid > Ibn ʿUmar

[Machine] The Messenger of Allah performed Umrah four times, one of them in the month of Rajab.  

الطبراني:١٣٥٢٣ – حَدَّثَنَا إِبْرَاهِيمُ بْنُ أَحْمَدَ الْوَكِيعِيُّ ثنا أَبِي ح وَحَدَّثَنَا أَحْمَدُ بْنُ شُعَيْبٍ أَبُو عَبْدِ الرَّحْمَنِ النَّسَائِيُّ أنا مُحَمَّدُ بْنُ رَافِعٍ النَّيْسَابُورِيُّ قَالَا ثنا يَحْيَى بْنُ آدَمَ عَنْ مُفَضَّلِ بْنِ مُهَلْهَلٍ عَنْ مَنْصُورٍ عَنْ مُجَاهِدٍ عَنِ ابْنِ عُمَرَ قَالَ

«اعْتَمَرَ رَسُولُ اللهِ ﷺ أَرْبَعَ عُمَرٍ إِحْدَاهُنَّ فِي رَجَبٍ»