What chemical can cause such a fire? A friend of mine who thinks that she is under influence of black magic met an astrologer. The astrologer asked her to wear a t-shirt for three nights and then bring that to him. The astrologer then cut some lemons and rubbed them throughout the t-shirt. Then he poured some water on her hands and face; and asked her to keep the t-shirt on her palm. After about 15 minutes, the y-shirt caught fire and the astrologer dropped the rest of water to put the fire down. 

I'm now wondering what chemical could cause this fire. I know that the water looked muddy. Would you please help me to find out what material was potentially used by the astrologer? I'm suspicious of the acid in the lemons and water which has been used, as well as body fat or sweat perhaps was on the t-shirt too. She was telling me that at first, smoke color was white but then it turned to black after the t-shirt caught fire. The smell of the fire was as bad as rotten meat.
White phosphorus can spontaneously ignite in air, and produces white smoke.  

Some oils, like linseed oil, on bunched-up cloth can also spontaneously combust.