Sayyiduna Abu Razin Laqit bin Amir Aqili رضي الله عنه said: I asked the Messenger of Allah صلى الله عليه وسلم: O Messenger of Allah! In the days of ignorance, we used to offer sacrifice in the month of Rajab. What is your opinion about this? He said: "There is no harm in slaughtering." (That is, when it is done for Allah, there is no objection to offering sacrifice in any month «كما فى النسائي وغيره» ). Imam Waki’ رحمه الله said: I never abandon this practice.
Hadith Referenceسنن دارمي / من كتاب الاضاحي / 2004
The mention of "Fara'" and "Atirah" has already passed above.
Fara' refers to the firstborn offspring of a she-camel, which used to be sacrificed in the names of idols and deities; this is prohibited (haram) in Islam. As for Atirah, this too was sacrificed for idols during the month of Rajab, so this is also deemed haram. However, if it is slaughtered in the name of Allah, then offering a sacrifice in the name of Allah is permissible in Rajab, Sha'ban, Ramadan, and every other month. Imam Waki‘ rahimahullah used to do likewise.