بسم الله الرحمن الرحيم
Imaam Muslim gathered and placed a narration, on the authority of Abu Hurairah, within his authentic compilation wherein the Prophet -sallahu alayhi wa sallam- said, “Whoever says:
لا إله إلا الله وحده لا شريك له، له الملك و له الحمد، و هو على كل شئ قدير
There is no deity in truth except Allah alone and without partners, to Him belongs the dominion and all praise, and He is Able to do all things, 100 times in a day, it is for him equal to the liberating of 10 slaves. Likewise 100 good deeds are written for him and 100 bad deeds are wiped away. It is also a protection for him from the devil that day until the evening. No one comes with that which is better than what he (who utters this) has come with, unless a person does more than this.
And whoever says:
سبحان الله و بحمده
Glorified is Allah and praises is to Him, 100 times in a day his sins will be diminished even if they are like the foam of the ocean.”
Imaam An-Nawawi said, “Contain therein is evidence regarding whoever says the tahleel more than 100 times in a day, there is for him the reward mentioned in the narration, and another reward as a result of an addition (to that amount). As this (saying it 100 times) is not a restriction that which prohibits transgressing and going beyond that amount, or that an increase (on that amount) has no virtue and is false, like an increase in the amount (of wiping the body limbs) for purification, or the raka’aat in the prayer.
It is possible that the intent is an increase in righteous actions, and not necessarily in saying the tahleel. Likewise it is possible that the intent is referring to an unrestricted increase regardless if it is in tahleel or in other than it (from righteous actions) and this possibility is more apparent, and Allah knows best.
Furthermore from the apparent generalization of the narration is that he, who said the tahleel 100 times in a day, obtains the previously mentioned rewards, regardless if it is (said) in sequence or in portions, or if he said some of it at the beginning of the day and some of it at the end of the day, however what is best is for one to do it consecutively at the beginning of the day in order for it to be a protection for him throughout the day.”
Translated by Najeeb ibn Yusuf Al Anjelesi
Source: صحيح مسلم بشرح النووي