I would really like to know about Sayyiduna Muhammad, sallallaahu alayhi wa sallam, what is the Du'a that everyday he had to say and loved to say, and that helped him through everything everyday?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The Prophet used to supplicate Allaah during the day and night by many different supplications, in which he asked Allaah for something and sought protection from some other things. Some of the supplications are mentioned here.

1- "Ya hayyu yaa qayyoom, birahmatika astagheeth, aslihlee sha'nee kullahu, wala takilnee ilaa nafsee tarfata 'Aayn." [At Tirmithi]

(O Ever Living, O Self-Subsisting and Supporter of all, by Your mercy I seek assistance, rectify for me all of my affairs and do not leave me to rely on myself, even for the blink of an eye).

2- "Allaahumma innee as-aluka Al-'afwa wal-'aafiyah, fid-dunya wal-aakhirah, allaahumma innee as-alukal-'aafwa wal-'aafiyah fee deenee, wa dunyaya wa ahlee, wa malee, allaahummastur 'awraatee, wa aamin raw'aatee, allaahummah-fathnee min bayni yadayya, wamin khalfee, wa'an yameenee, wa'an shimalee, wamin fawqee, wa-a'aoothu bi'athamatika an ughtala min tahtee." [Abu Daawood]

(O Allaah, I ask You for pardon and well-being in this life and the next. O Allaah, I ask You for pardon and well-being in my religious and worldly affairs, and my family and my wealth. O Allaah, veil my weaknesses and set at ease my dismay. O Allaah, preserve me from the front and from behind and on my right and on my left and from above, and I take refuge with You lest I be swallowed up by the earth).

Ibn 'Umar said: "The Prophet never gave up supplicating these supplications in the evening and in the morning."

3- "Allaahumma 'aafinee fee badanee, allaahumma 'aafinee fee sam'ee, allaahumma 'aafinee fee basaree, laa ilaaha illa ant. Allaahumma innee a'aoothu bika minal-kufri, walfaqri, allaahumma innee a'aoothu bika min 'athaabil-qabr." (Three times in the morning and in the evening).[Abu Daawood]

(O Allaah, grant my body health, O Allaah, grant my hearing health, O Allaah, grant my sight health.  None has the right to be worshipped except You. O Allaah, I take refuge with You from disbelief and poverty, and O Allaah I take refuge with You from the punishment of the grave.  None has the right to be worshipped except You. O Allaah, I take refuge with You from disbelief and poverty, and I take refuge with You from the punishment of the grave.  None has the right to be worshipped except You) (Three times).

Finally, we advise you to refer to the books or supplications in order to know more supplications that were recited by the Prophet in the morning and in the evening.

For instance, Hisn al-Muslim written by Shaykh Sa'eed Al-Qahtaani, may Allaah preserve him, is a short and authentic book on this subject. It is translated into English and many other languages, so we advise you to acquire it.

Allaah Knows best.