The Messenger of Allah (may Allah’s peace and blessings be upon him) was asked about the foremost deed that leads people to Paradise, and he replied: Fear of Allah and good character. Then, he was asked about the most things that lead people into Hellfire, and he said: The tongue and the private parts
Good chain of narratorsعن أبي هريرة رضي الله عنه قال: سئل رسول الله صلى الله عليه وسلم عن أكثر ما يُدْخِلُ الناسَ الجنة؟ قال: «تقوى الله وحسن الخلق»، وسئل عن أكثر ما يُدْخِلُ الناسَ النار، فقال: «الفم والفرج».
Abu Hurayrah (may Allah be pleased with him) reported: The Messenger of Allah (may Allah’s peace and blessings be upon him) was asked about the foremost deed that leads people to Paradise, and he replied: "Fear of Allah and good character." Then, he was asked about the most things that lead people into Hellfire, and he said: "The tongue and the private parts."
Explanation
The most means leading people to Paradise are fear of Allah and good manners. To fear Allah is to shun all kinds of prohibitions, and good character is shown in dealing with people; and the least of it is to avoid harming others, while the highest of it is doing good to the one who misbehaved with you. On the other hand, the most causes that lead people into Hellfire are the mouth and the private parts, which often prompt one to exceed the limits concerning his Lord and the people.
Source · Narrated by Ibn Majah - Narrated by At-Termedhy - Narrated by Ahmad
From the Hadith Encyclopedia (hadeethenc.com).