Just as in Dar-ul-Arqam, the Muslims in Madinah needed education. After the construction of Masjid an-Nabawi, Al-Suffah was established—a raised platform outside the mosque where Companions gathered to learn. Due to his busy schedule, the Prophet Muhammad ﷺ entrusted the students of Suffah to Ubadah bin As-Samit (RA), making him their teacher. He taught them Quranic recitation along with the art of writing.
In addition to Quranic recitation, Ubadah (RA) was an expert in Hadith and actively spread the Prophet's ﷺ teachings, even reciting them to Muslims and Christians when visiting churches. Imam Bukhari narrated numerous Ahadith through him. He also possessed immense expertise in Islamic jurisprudence (Fiqh) and prioritized religion above all personal ties.
When the Battle of Badr took place in 2 AH, he joined the 313 blessed companions. Following Badr, when the tribe of Banu Qaynuqa intended to rebel, the Prophet ﷺ ordered their expulsion. Banu Qaynuqa hoped Ubadah (RA) would interdict for them due to their long-standing alliance and his close relation to the Prophet ﷺ, but out of pure love for Allah and His Messenger ﷺ, Ubadah (RA) severed all ties with them and refused to intercede for rebels.
He also participated in the Pledge of Ridwan (Bai'at-e-Ridwan). Towards the end of the Prophet’s ﷺ life, when appointed as an administrator, the Prophet ﷺ advised him: "Fear Allah, lest on the Day of Judgment an animal brings a complaint against you before Him." Hearing this, Ubadah (RA) vowed: "By Allah, I do not desire to rule over even two men," fulfilling the duty purely out of obedience to the Prophet's ﷺ command.
After the passing of the Prophet ﷺ, during the Caliphate of Abu Bakr Al-Siddiq (RA), Ubadah (RA) participated in the battles of Syria. He continued his military efforts during the era of Umar Al-Farooq (RA). When Amr bin Al-Aas (RA) faced difficulty in opening Egypt, he requested reinforcements from Caliph Umar (RA). Umar (RA) dispatched a force of 4,000 men with four commanders, stating that each commander was equivalent to a thousand troops himself. Ubadah (RA) was one of those four commanders.
Upon the arrival of reinforcements in Egypt, Amr bin Al-Aas (RA) welcomed them with great joy. He asked Ubadah (RA) for his spear, wrapped his own turban around it to create the supreme commander's banner, and handed it to him, declaring: "This is the banner of leadership; today you are the commander of this army." Ubadah (RA) took the banner, organized the troops, and launched an attack. By Allah’s grace, Egypt was conquered in the very first assault.