The teacher asks them to send blessings upon the Prophet 300 times before each lesson

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Is it Sunnah to say Laa ilaaha ill-Allaah when parting from one’s friend?
Guidelines on shar’i wird

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Related Answers:
There is no specific du’aa’ to be recited before reading Qur’aan
Specifying a number of times to recite dhikr or du’aa’ that is not narrated in sharee’ah
Ruling on reading Soorat Yaa-Seen for the dying and the deceased
Is it Sunnah to say Laa ilaaha ill-Allaah when parting from one’s friend?
Guidelines on shar’i wird

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