Abu Ayyub Al-Ansari (May Allah be pleased with him) reported:
The Prophet (Sallallahu Alaihi Wasallam) said:
“He who utters ten times: `
La ilaha illallahu,

wahdahu la sharika lahu,
lahulmulku wa lahulhamdu,

wa Huwa `ala kulli sha’in Qadir
(there is no true god except Allah. He is One and He has
no partner with Him. His is the sovereignty and His is the praise,
and He is Omnipotent),’
he will have a reward equal to that for freeing four slaves
from the progeny of Prophet Isma`il.”
[Al-Bukhari and Muslim].

Commentary:
“Slaves from the progeny of Isma`il” is a simile for very
precious slaves. That is, it has the same reward to which
the emancipation of four very precious slaves is eligible.