What is the concept of friendship in Islam, and what are the characteristics of a good friend?

Friendship is companionship based on love and sincerity. Islamic law encourages befriending the righteous and avoiding befriending the wicked, as the Prophet, peace and blessings be upon him, said: "A person is upon the religion of his friend, so let one of you look at whom he befriends," and he also said: "The example of a good companion and a bad companion is like the seller of musk and the blower of the bellows." A good friend should possess qualities of loyalty, trustworthiness, sincerity, generosity, and praise. If friendship is not based on obedience (to Allah), it will turn into enmity on the Day of Resurrection, as Allah Almighty says: "Close friends on that Day will be enemies to each other, except for the righteous."