What is the ruling on the statement of one of the Tabi'in: "If I were to reproach a man for suckling a dog, I would fear suckling a dog myself"? And is it authentic?

The phrase "Calamity is entrusted to speech" was narrated as مرفوعة (marfu'ah - directly attributed) to the Prophet, peace and blessings be upon him, but it is not authentic. Its weakness was noted by Ibn al-Jawzi, Ibn Rajab, and Al-Albani.

It was narrated from Abdullah ibn Mas'ud that he said: "If I were to ridicule a dog, I would fear becoming a dog."

Likewise, Abu Musa al-Ash'ari said: "If I saw a man suckling a ewe on the road, and I ridiculed him, I would fear that I would not die until I suckled it myself."

Generally, these narrations indicate a warning against gloating, and that the gloater may be punished with that which he gloated about.

It was mentioned in the Hadith (definition): "Do not express schadenfreude towards your brother, for Allah will have mercy on him and afflict you."

Ibn al-Qayyim said: "Whoever makes another cry, will be cried upon; whoever laughs at people, will be laughed at; and whoever shames his brother for an act, will inevitably be afflicted by it."

Ibn Rajab said: "Whoever spreads evil about his believing brother, pursues his faults, and exposes his nakedness, Allah will pursue his nakedness and expose him."

Al-Hasan (definition) said: "It used to be said: Whoever shames his brother for a sin from which he repented, will not die until Allah afflicts him with it."