God gave you victory at Badr when you were weak; fear God and perhaps you will be grateful.
When you said to the Believers, "Is it not enough that God reinforced you with three thousand angels sent down?—Holy Qur'an, Sura 3 (Al ‘Imran), 123
It is proving to be another violent Ramadan, with violent jihadi attacks in Kuwait and Sousse and Grenoble, and today's assassination in Cairo. Ramadan is meant to be a month of peace and reconciliation, and warring Muslim states have sometimes held cease-fires during Ramadan, but in fact there is no outright prohibition on fighting during Ramadan, a fact jihadists use to step up violence in what they see as a holy war against those they see as enemies, even their fellow Muslims.
The precedent lay in the very earliest years of Islam, just two years after the Prophet's hijra from Mecca to Medina. In AH 2 (AD 634), the Prophet Muhammad and his small Muslim forces fought against the more powerful Meccans in their first great battle, at Badr. It is one of the few battles mentioned by name in the Qur'an (above), which attributes the victory to Divine intervention. The traditional date of Badr is the 17th of Ramadan, AH 2.
Nor was Badr that unusual. Saladin's defeat of the Crusaders at Hattin in 1187 was also in Ramadan, and in Muslim tradition is said to have taken place the morning after the Laylat al-Qadr. (See the link for explanation.)
Less than a century later in 1260, the Mamluks finally stopped the Mongol invasion of the Middle East at another Battle in Galilee, at ‘Ain Jalut, fought in Ramadan.
On October 6, 1973, Egypt and Syria launched the 1973 Arab-Israeli War. The crossing of the Suez Canal may be remembered for taking place on Yom Kippur, but it was also the 10th of Ramadan. A code name for the Canal crossing was, in fact, Operation Badr. One of Egypt's satellite cities near Cairo is named 10th of Ramadan.
And during the Iran-Iraq War Iran even named an offensive which it launched in Ramadan the Ramadan Offensive.
Most Muslims would prefer not to fight in Ramadan, but there are numerous precedents, and in recent years jihadist terror violence has often spiked in Ramadan.