Nu'aim b. Mas'ud reported God's Messenger as saying to two men who came from Musailima, "I swear by God that were it not that messengers are not killed, I would cut off your heads.”
Quraish sent me to God’s Messenger and when I saw him Islam was cast into my heart, so I said, "Messenger of God, I swear by God that I shall never return to them.” He replied, "I do not break a covenant or imprison messengers; but return, and if you feel the same as you do just now, come back.” So I went away and then came to the Prophet and accepted Islam.
‘Amr b. Shu'aib, on his father’s authority, told that his grandfather reported God’s Messenger as saying in the course of his sermon, "Observe fully the alliance made in the pre-Islamic period, for it, i.e. Islam, will only make it stronger; but make no new alliances in Islam.”
There was a covenant between Mu'awiya and the Byzantines, and he was going towards their country; then when the covenant came to an end he attacked them. A man came on a horse, or a packhorse, saying, “God is most great, God is most great; let there be faithfulness and not treachery.”* And when they looked they found that he was 'Amr b. ‘Abasa. Mu'awiya questioned him about that and he replied that he had heard God’s Messenger say, "When one has a covenant with people he must not loosen or strengthen it till its term comes, or he brings it to an end in agreement with them.” He said that Mu'awiya then took the people back.
*Mirqat, 4, 255 says that 'Amr b. ‘Abasa felt it was an act of treachery to make a treaty while in one’s own country and then approach the enemy’s country when the period of the treaty was near an end, so as to be able to make an immediate attack.
