The best number of companions is four; the best detachment is (that made up of) four hundred; and the best army is (that made up of) four thousand; and an army of twelve thousand will never be defeated because of their small numbers
Authentic hadithعن ابن عباس رضي الله عنهما مرفوعاً: «خير الصحابة أربعة، وخير السَّرَايَا أَرْبَعُمِائة، وخير الجيوش أربعة آلاف، ولن يُغْلَبَ اثنا عشر ألفا مِنْ قِلَّةٍ»
Ibn ‘Abbās (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "The best number of companions is four; the best detachment is (that made up of) four hundred; and the best army is (that made up of) four thousand; and twelve thousand men will never be defeated because of their small numbers."
Explanation
Explanation: The best companionship is that made up of four persons; and the best detachment consists of four hundred soldiers; and the most helpful soldiers are those that have reached four thousand. If an army reaches twelve thousand soldiers, it will not be defeated. If it is defeated, then it will not be due to its small number; rather it might be defeated for some other reasons, such as lack of religious commitment, feeling proud of their large number, committing sins, absence of sincerity to Allah, etc.
Source · Narrated by At-Termedhy - Narrated by Abu Daoud - Narrated by Ahmad
From the Hadith Encyclopedia (hadeethenc.com).