What is the authenticity of the hadith which states that whoever says upon going to sleep: "I seek forgiveness from Allah, the Almighty, whom there is none worthy of worship except Him, the Ever-Living, the Sustainer, and I repent to Him" three times, his sins will be forgiven even if they were like the foam of the sea, and is acting upon it considered Sunnah?

The aforementioned Hadith (definition): "Whoever says when he goes to bed: 'I seek forgiveness from Allah, the Magnificent, whom there is no god but He, the Living, the Sustainer, and I repent to Him' three times, Allah will forgive his sins, even if they are like the foam of the sea..." was narrated by Al-Tirmidhi, but its chain of narration is weak. He narrated it through Ubaidullah bin Al-Walid Al-Wassafi, who is weak, from Atiyyah Al-Awfi, who is truthful but makes many mistakes and is a mudallis (one who conceals defects in a Hadith chain). It was weakened by Al-Albani.

However, the virtue of this dhikr (remembrance) is mentioned in other authentic Ahadith, among them what Al-Tirmidhi narrated and Al-Albani authenticated: "Whoever says: 'I seek forgiveness from Allah, the Magnificent, whom there is no god but He, the Living, the Sustainer, and I repent to Him,' he will be forgiven, even if he fled from the battlefield."

There is no harm in acting upon the aforementioned weak Hadith regarding the virtues of deeds, provided it is not attributed to the Prophet (peace be upon him), as long as the act itself is originally established by authentic evidence.