Classical Sunni sources preserve reports that al-Bara ibn Malik may Allah be pleased with him was among those whose oath to Allah was fulfilled. In a major battle against the Persians, the Muslims asked him to swear by his Lord for victory, and he prayed that Allah grant them victory over the enemy. The report says the enemy was defeated; in a later critical encounter al-Bara again prayed for victory and added that Allah join him with His Prophet, after which victory came and al-Bara was killed as a martyr. Al-Tirmidhi grades the general virtue report hasan gharib, and al-Hakim grades the battle route sahih al-isnad.
In one major battle against the Persians, the Muslims are reported to have suffered heavily. They then turned to al-Bara and asked him to swear by his Lord for victory. Al-Bara responded with a prayer in oath-like wording, asking Allah to grant the Muslims the enemy's shoulders or victory over them. The report then states that the enemy was defeated after his supplication.
A later critical encounter preserves a similar but more personal prayer. Al-Bara again asked Allah for victory for the Muslims, but this time he added a request that Allah join him with His Prophet. The narration then gives a double outcome: the Muslims were granted victory, and al-Bara himself was killed as a martyr. In the structure of the report, the military victory and his own martyrdom are presented together as the fulfillment of that second supplication.
The battle sequence is preserved by al-Hakim through al-Zuhri from Anas, and al-Hakim grades the report sahih al-isnad. Ibn Hajar also preserves the battle material in his biographical treatment of al-Bara, and al-Lalaka'i includes the event within the karamat of al-Bara ibn Malik. These sources support the event as more than a late devotional anecdote.
The strongest evidence-based conclusion is therefore direct. The source set preserves a recognized Prophetic virtue associated with al-Bara, a battlefield supplication for victory followed by defeat of the enemy, and a later prayer combining victory with martyrdom followed by both outcomes. The exact year of his death should not be forced where historical accounts differ, but the prayer-and-fulfillment sequence itself has strong classical support and warrants high-confidence inclusion.
Conclusion
Classical Sunni sources strongly preserve reports that al-Bara ibn Malik prayed for Muslim victory, saw that victory follow, and in a later encounter prayed both for victory and for martyrdom, after which both were reported to occur. The combined source support justifies high-confidence inclusion as a companion karamah centered on accepted prayer.