As for gambling with eggs, selling them to those who gamble with them, or buying them from gamblers, the ruling is clear. These practices also include women taking olive leaves or washing with olive-leaf water, for this originates in baptismal water.
They also include suspending regular activities in crafts, trade, or study circles during their festivals, making the occasion a day of rest and rejoicing, and other such practices. The Prophet, may Allah bless him and grant him peace, forbade them to observe the two days on which they used to amuse themselves in pre-Islamic times. He also forbade slaughtering animals in a place where the polytheists used to worship.
They do things that make the believer’s heart shudder—a believer whose heart has not died, but who recognizes what is right and rejects what is wrong. Just as one must not imitate them, a Muslim who imitates them must not be helped to do so; rather, he must be told not to.
If someone holds a feast during their festivals that departs from his usual practice, his invitation should not be accepted. If a Muslim gives a gift during these festivals that departs from his usual practice at other times, his gift should not be accepted, especially if it helps people imitate them. Examples include giving candles and the like at Christmas, or giving eggs, milk, and sheep on “Little Thursday” at the end of their fast—that contemptible Thursday. Nor