The one he ﷺ told Muʿādh never to leave
He took him by the hand, said he loved him, and told him not to drop this after any prayer.
أُوصِيكَ يَا مُعَاذُ لاَ تَدَعَنَّ فِي دُبُرِ كُلِّ صَلاَةٍ تَقُولُ اللَّهُمَّ أَعِنِّي عَلَى ذِكْرِكَ وَشُكْرِكَ وَحُسْنِ عِبَادَتِكَ
Allāhumma aʿinnī ʿalā dhikrika wa shukrika wa ḥusni ʿibādatik.
“O Allah, help me to remember You, to thank You, and to worship You well.”
Notice it asks for help with the asking itself. Even remembering Him is something you need His help to do.
The full narration
Mu'adh b. Jabal reported that the Messenger of Allah (ﷺ) caught his hand and said:By Allah, I love you, Mu'adh. I give some instruction to you. Never leave to recite this supplication after every (prescribed) prayer: "O Allah, help me in remembering You, in giving You thanks, and worshipping You well." Mu'adh willed this supplication to the narrator al-Sunabihi and al-Sunabihi to 'Abu Abd al-Rahman
Source
Sunan Abī Dāwūd · 1522
- Al-Albani: Sahih
- Muhammad Muhyi Al-Din Abdul Hamid: Sahih
- Shuaib Al Arnaut: Sahih
- Zubair Ali Zai: Isnaad Sahih