Sahih Muslim
The Book of Zakat (Kitab Al-Zakat)
Book Number: 005 / Hadith Number: 2164
This hadith has been narrated by Suhail b. Abu Salih with the same chain of transmitters, and he said he substituted the word aqsa' with 'adba' and said:" his side and his back," but he made no mention of his forehead.