Concept:Selfishness is discouraged by showing mercy and compassion to others.Explanation:Hadith 21 of An-Nawawi's selected sayings teaches this lesson clearly.It states: "Have mercy on those who are on earth, and the One in the heavens will have mercy on you."This means that genuine faith requires a believer to care about the welfare of others, not only himself.A selfish person ignores the needs of people around him, while this hadith calls for kindness and consideration.Therefore, it directly discourages selfish tendencies.Answer:D. twenty one