Hadith: 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

عن ابن عباس رضي الله عنهما مرفوعاً: «خير الصحابة أربعة، وخير السَّرَايَا أَرْبَعُمِائة، وخير الجيوش أربعة آلاف، ولن يُغْلَبَ اثنا عشر ألفا مِنْ قِلَّةٍ»
[صحيح] - [رواه أبو داود والترمذي وأحمد]

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."
[Authentic hadith] - [Narrated by At-Termedhy - Narrated by Abu Daoud - Narrated by Ahmad]

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.