Using something as a reminder

It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that "whenever the Messenger of Allah (peace and blessings be upon him) feared that he (peace and blessings be upon him) would forget something, he (peace and blessings be upon him) would tie a thread on his blessed hand so that he could remember that matter by its help and it would serve as a reminder for him (peace and blessings be upon him)."
Al-Harith bin Abi Usamah recorded it in his Musnad; its chain contains a narrator named Anbasah bin Abd al-Rahman, who is matruk al-hadith (abandoned in hadith) and severely da'if (weak), on account of which this report is extremely weak and unreliable in its chain.

It is narrated from a man of Banu Tamim that the Messenger of Allah (peace and blessings be upon him) said: "When one of you fears that he will forget (something or some knowledge), let him recite this supplication: 'Al-hamdu lillahi mudhakkiri al-nasi' (All praise is for Allah, who reminds the one who forgets)."
The chain of this hadith is da'if (weak), because one of its narrators, Mu'awiyah bin Yahya, is weak, and the man of Banu Tamim from whom he narrated is majhul (unknown).