Anyone who takes a false oath at this pulpit of mine, even concerning a green tooth-stick, will surely occupy his seat in Hell
Authentic hadithعن جابر بن عبد الله قال: قال رسول الله صلى الله عليه وسلم : «لا يحْلِفُ أحدٌ عند مِنْبَرِي هذا على يَمينٍ آثِمَة، ولو على سِواكٍ أَخْضَرَ، إلا تَبَوَّأَ مَقْعَدَه مِن النار -أو وَجَبَتْ له النار-».
Jābir ibn ‘Abdullāh (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: ''Anyone who takes a false oath at this pulpit of mine, even concerning a green tooth-stick, will surely occupy his seat in Hell – or he will surely enter Hell.''
Explanation
In this Hadīth, Jābir (may Allah be pleased with him) says that the Prophet (may Allah's peace and blessings be upon him) clarified how grave a sin it is to swear a false oath at the Prophet's pulpit in his mosque, even concerning a trivial matter. Indeed, in this place, the Prophet (may Allah's peace and blessings be upon him) is to be glorified, and what he said on the pulpit is to be remembered. So, going against his teachings by taking a false oath makes one deserving of this threat. A false oath entails the wrath of Allah, but in such an honorable place (as the Prophet's pulpit inside his mosque) it is an uglier sin.
Source · Narrated by Ibn Majah - Narrated by Abu Daoud - Narrated by Ahmad - Maalik
From the Hadith Encyclopedia (hadeethenc.com).