Al-Kāfi - Volume 4 > The Months in Which Al-’Umrah Is Preferable and the Case of One Who Assumes the State of Ihram in One Month and Comes Out of Such State in another Month
Hadith #6

6ـ مُحَمَّدُ بْنُ إِسْمَاعِيلَ عَنِ الْفَضْلِ بْنِ شَاذَانَ عَنْ صَفْوَانَ بْنِ يَحْيَى عَنْ مُعَاوِيَةَ بْنِ عَمَّارٍ عَنْ أَبِي عَبْدِ الله (عَلَيْهِ السَّلاَم) قَالَ الْمُعْتَمِرُ يَعْتَمِرُ فِي أَيِّ شُهُورِ السَّنَةِ شَاءَ وَأَفْضَلُ الْعُمْرَةِ عُمْرَةُ رَجَبٍ.

6. Muhammad ibn Isma‘il has narrated from al-Fadl ibn Shadhan from Safwan ibn Yahya from Mu‘awiyah ibn ‘Ammar who has said the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, has said that one may perform al-‘Umrah during any month of the year. The excellent al-‘Umrah is during the month of Rajab.”