Mukhtasar Sahih Bukhari — Hadith 2086

It is narrated from Sayyiduna Abu Ayyub Ansari and Ibn Mas'ud (may Allah be pleased with them) that the Prophet Muhammad (peace and blessings be upon him) said: "Whoever recites the above-mentioned phrase (the declaration of faith: La ilaha illallah...) ten times, will receive a reward as if he has freed one slave from the descendants of Isma'il (peace be upon him)."