I never failed to join Allah's Apostle in any of his Ghazawat except in the Ghazwa of Tabuk. However, I did not take part in the Ghazwa of Badr, but none who failed to take part in it, was blamed, for Allah's Apostle had gone out to meet the caravans of (Quraish, but Allah caused them (i.e. Muslims) to meet their enemy unexpectedly (with no previous intention) .
That he heard the Prophet saying, "It is not permissible for a man to be alone with a woman, and no lady should travel except with a Muhram (i.e. her husband or a person whom she cannot marry in any case for ever; e.g. her father, brother, etc.)." Then a man got up and said, "O Allah's Apostle! I have enlisted in the army for such-and-such Ghazwa and my wife is proceeding for Hajj." Allah's Apostle said, "Go, and perform the Hajj with your wife."
The believers who failed to join the Ghazwa of Badr and those who took part in it are not equal (in reward).