Through ransoms paid for kidnapped Westerners. Kidnapping infidels and releasing them for ransom is fully sanctioned in Islamic law: "As for the captives, the amir [ruler] has the choice of taking the most beneficial action of four possibilities: the first to put them to death by cutting their necks; the second, to enslave them and apply the laws of slavery regarding their sale and manumission; the third, to ransom them in exchange for goods or prisoners; and fourth, to show favor to them and pardon them. Allah, may he be exalted, says, 'When you encounter those [infidels] who deny [the Truth=Islam] then strike [their] necks' (Qur'an sura 47, verse 4)" — Abu’l-Hasan al-Mawardi, al-Ahkam as-Sultaniyyah (The Laws of Islamic Governance), trans. by Dr. Asadullah Yate, (London), Ta-Ha Publishers Ltd., 1996, p. 192.
"Millions in Ransoms Fuel Militants’ Clout in West Africa," by Adam Nossiter in the New York Times, December 12 (thanks to Twostellas):
BAMAKO, Mali — Oumar Ould Hamaha, a notorious Islamist commander in the deserts of western Africa, has nothing but disdain for the international powers he opposes or the hapless Westerners he and other militants subject to extreme deprivation, hunger, thirst and proselytizing for months on end.
But he openly appreciates them for helping Islamists acquire the one thing they cannot do without.
“Lots of Western countries are paying enormous sums to the jihadists,” he said in a telephone interview from northern Mali, crowing about the hefty ransoms militants have collected in the region. “The source of our financing is the Western countries. They are paying for jihad.”
Kidnapping is such a lucrative industry for extremists in western Africa, netting them tens of millions of dollars in recent years, that it has reinforced their control over northern Mali and greatly complicated plans for an African-led military campaign to take back Islamist-held territory.
Beyond the immediate risk to the 10 Europeans and 3 Algerians still being held — “At the first strike, the hostages will have their throats cut like chickens, one after the other,” Mr. Hamaha threatened — an intervention could face formidable opponents. Al Qaeda in the Islamic Maghreb, one of the factions that have seized northern Mali, is estimated to have amassed as much as $90 million or more in ransoms over the past decade, turning it into one of the region’s wealthiest, best-armed militant groups....
Mr. Hamaha was with Al Qaeda in the Islamic Maghreb when he helped kidnap a Canadian diplomat, Robert Fowler, late one December afternoon in 2008 outside the capital of Niger, Niamey. Now the jihadist says he is “in charge of security” for the Malian offshoot of Al Qaeda in the Islamic Maghreb, Mujao, the Movement for Oneness and Jihad in West Africa, another of the three radical groups that control northern Mali....
Mr. Hamaha, his captor, who takes calls from reporters, said: “Ah yes, the Canadian that we kidnapped. I don’t regret it at all. He was in a state of being lost,” referring to what he considered the Westerner’s perilous spiritual condition. The Canadian, Mr. Hamaha said, “learned many things from us.”
During his captivity Mr. Fowler, who was the United Nations special envoy to Niger, gained perhaps the sharpest insight yet into the mentality of some of the men who now hold northern Mali. “There’s no doubt of their faith: they would sit chanting in the full Sahara sun for hour after hour.”