Question: What is the ruling on saying any formula of Thikr (remembrance of Allaah) in a specific number of times? How can it be impermissible while there are the two following Hadeeth: If anyone invokes blessings on me once on Friday, Allaah will bless them ten times, and whoever invokes blessings on me ten times, Allaah will bless them one hundred times and Whoever says: ‘There is none worthy of worship (in truth) but Allaah. He is alone, Who has no partner. To Him belongs the sovereignty and to Him praise is due. He gives life and causes death and He is Potent over everything,’ a hundred times every day, they will get the reward of emancipating one thousand persons from the progeny of Ismaa`eel (Ishmael) ?
Answer: It is desirable to say the formulae of Thikr for a specific number of times, if this is stated in the Share`ah (Islaamic law). Regarding the formulae of Thikr for which there is no mention of a specific number of times, it is permissible to say them without being bound by a specific number. Accordingly, this permissibility does not contradict the authenticity of the Ahaadeeth mentioned above… read more here.