From Sahih Muslim (Hadith 5797):
Jabir b. 'Abdullah reported Allah's Apostle (ﷺ) as saying:There is no transitive disease, no safar, no ghoul. He (the narrator) said: I heard Abu Zubair say: Jabir explained for them the word safar. Abu Zubair said: safar means belly. It was said to Jabir: Why is it so? He said that it was held that safar implied the worms of the belly, but he gave no explanation of ghoul. Abu Zubair said: Ghoul is that which kills the travellers
Reference: Muslim 5797