Chickens is usually killed to celebrate Christmas in Nigeria. Thus, is it allowed for a Muslim who coincidentally have chickens to sell at this period (without intention of Christmas) to move with his business, knowing that most of the purchaser will kill it for Christmas.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

In principle, trade is permissible; Allah Says (what means): {But Allah has permitted trade and has forbidden interest.} [Quran 2:275]

However, if the sale is accompanied by some kind of helping in evil, then the sale becomes forbidden. The jurists stated that it is prohibited to sell to the polytheists what helps them in their festivals, such as meat and others.

Ibn Taymiyyah said in Iqtidhaa’ As-Siraat Al-Mustaqeem:

"Is it not permissible for Muslims to sell to the Christians anything that helps them to celebrate their festival; neither meat, nor food, nor dress. They should not loan their riding-beasts to them or help them in any way with their festival, because this is a form of honoring their Shirk and helping them with their Kufr (disbelief). The authorities should prevent Muslims from doing this. This is the view of Imaam Maalik and others, and I do not know of any opinion which contradicted this." [End of quote]

Therefore, whoever knows that someone will slaughter the chicken to celebrate the Christian festival, then it is forbidden to sell it to him, because selling it to him is helping him commit something evil.

Allah knows best.