The Chovos Halevavos famously writes, Yichud Hama’seh chapter 5:
ואמרו על חסיד, שפגע אנשים שבים ממלחמת אויבים, ושללו שלל אחר מלחמה חזקה, אמר להם: שבתם מן המלחמה הקטנה שוללים שלל, התעתדו למלחמה הגדולה. אמרו לו: ומה היא המלחמה הגדולה? אמר להם: מלחמת היצר וחייליו.
But this story was first told of Mohammed. He is the “Chassid” referred to above. The warriors he met were his own. “Jihad” is the word for “war”, both lesser and greater. For a full discussion see this.
Nor is this the only example of Rabbi Bachye borrowing from their material. Know the one about the carcass’ white teeth? See Otzar Hachochma Forums here on that. Others were similarly influenced, including Rabbi Avraham ben Harambam, who incorporated silly Sufism in his syncretistic “Hamaspik Le’ovdei Hashem”. For a too-wide overview, see this.
There are a whole host of lessons to be learned here. The easiest to ignore is this: the brand of of “piety” sought by the author of “Chovos Halevavos” is not a Jewish one. This is blatantly obvious from the author’s introduction as well.
I hope to elaborate at some future date.