According to rahyafte (the missionaries and converts website):The most rewarding form of seeking forgiveness is reciting it after the Asr prayer. If done daily, angels are tasked with tearing apart the letter of misdeeds of the repentant.
The Messenger of Allah (PBUH) said: “Whoever says once after the Asr prayer every day:
“أَسْتَغْفِرُ اللهَ الَّذِي لا إِلٰهَ إِلَّا هُوَ الْحَيُّ الْقَيُّومُ، الرَّحْمَٰنُ الرَّحِيمُ، ذُو الْجَلَالِ وَ الْإِكْرَامِ، وَ أَسْأَلُهُ أَنْ يَتُوبَ عَلَيَّ تَوْبَةَ عَبْدِ ذَلِيلٍ خَاضِعٍ فَقِيرٍ بَائِسٍ مَسْكِينٍ (مُسْتَكِينٍ) مُسْتَجِيرٍ لَا يَمْلِكُ لِنَفْسِهِ نَفْعًا وَ لَا ضَرًّا وَ لَا مَوْتًا وَ لَا حَيَاةً وَ لَا نُشُورًا.”
“I seek forgiveness from Allah, the One besides whom there is no deity, the Ever-Living, the Sustainer of existence, the Most Gracious, the Most Merciful, the Possessor of Majesty and Honor. I ask Him to grant me a repentance like that of a humble, submissive, poor, destitute, and seeking refuge servant who has no control over his own benefit, harm, life, death, or resurrection.”
Allah orders two angels assigned to the person to tear apart, whatever it may be, the letter of his misdeeds.
Mustadrak al-Wasail, Vol. 5, p. 120
