Sahih Bukhari 4376 — The delegation of Banu Hanifa and the narration

Narrated Abu Raja Al-Utaridi: We used to worship stones, and when we found a better stone than the first one, we would throw the first one and take the latter, but if we could not get a stone then we would collect some earth (i.e. soil) and then bring a sheep and milk that sheep over it, and perform the Tawaf around it. When the month of Rajab came, we used (to stop the military actions), calling this month the iron remover, for we used to remove and throw away the iron parts of every spear and arrow in the month of Rajab.