[Surah Al-Qalam 68:4]
The Prophet ﷺ was asked, “Who is the best amongst people?”
He replied, “The best of people are those who are most beneficial to people.”
The Prophet ﷺ was mercy for all, hence it is expected that all of his followers would be merciful and kind to others.
The Mercy of Allah encompasses all of his creation.
The advice and teachings of being kind and merciful to others will remain true till the Day of Judgement for all the followers of the Prophet ﷺ. His mercy cannot be restricted.
A man prayed to Allah, “O Allah! Show mercy to me and Mohammed and not to anyone else.”
The Prophet ﷺ corrected him, “Do not make such dua but ask Him to show mercy to all.”
As Ashraful Makhloqaat (اشرف المخلوقات), The Best of all creations, humans should show good conduct towards all animals
Ibn Umar (May Allah be pleased with him) narrates a hadith:
The Prophet (ﷺ) said, "A woman entered the (Hell) Fire because of a cat which she had tied, neither giving it food nor setting it free to eat from the vermin of the earth.Sahih Bukhari 3318
Scholars have explained that she was a believing woman but she entered Hell Fire because of her cruelty towards animals
Imam Bukhari notes a narration in his al Adab al Mufrad:
Abu Umama narrates: “Whoever slaughters an animal or a fowl, and shows mercy by sharpening the knife properly so that the animal may be spared from suffering, Allah would show mercy to him on the Day of Judgement.”