Hadithcore
Riyad as-Salihin, 1514

Abu Hurairah (May Allah be pleased with him) reported:

I heard the Prophet (ﷺ) saying, "A person utters a word thoughtlessly (i.e., without thinking about its being good or not) and, as a result of this, he will fall down into the fire of Hell deeper than the distance between the east and the west." <b>[Al-Bukhari and Muslim]</b>.

وعن أبي هريرة رضي الله عنه أنه سمع النبي صلى الله عليه وسلم يقول‏:‏ “إن العبد ليتكلم بالكلمة ما يتبين فيها يزل بها إلى النار أبعد مما بين المشرق والمغرب‏"‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏ ‏ ‏ومعني‏:‏ ‏ ‏يتبين‏ ‏ يتفكر أنها خير أم لا.‏

References1 variant
In-Book Reference
Book 17, Hadith 4
Sharh · explanationclick to expand
<b>Guidance from the Hadiths:</b><br> 1) A Muslim is encouraged to ponder on and think about his words so that he would speak only when this may result in realization of interest and good things, otherwise, he should not.<br> 2) There are levels in Paradise and depths in Hell. Every person is going to attain his position according to his deeds, and by the favor and justice of Allah.<br> 3) There is a warning against intense heedlessness, as it entails the displeasure of Allah Almighty and the threat of the torment of Hell.<br> 4) Demonstrating the magnificent mercy of Allah Almighty and His favor upon his slaves, as he accepts from them simple deeds and gives them in return ample rewards.