All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Performing the prayer at its prescribed fixed time is one of the best actions in the sight of Allah, the Great and Almighty, and it is the most beneficial action to His servants. In a sound Hadeeth, 'Abdullah Ibn Mas'ood asked the Prophet about the most beloved action to Allah and he (the Prophet) replied: “Performing the prayer at its beginning time”. 'Abdullah asked: 'Then what?' The Prophet said: “To treat parents righteously”. Abdullah asked: 'Then what is next? The Prophet said: “Making Jihad for the sake of Allah”. [Al-Bukhari and Muslim] In the same vein, Allah Says (what means): {And when you have completed the prayer, remember Allah standing, sitting, or [lying] on your sides. But when you become secure, re-establish [regular] prayer. Indeed, prayer has been decreed upon the believers a decree of specified times.} [Quran 4:103]. According to our revered scholars, this verse refers to those who delay the prayer. Therefore, dear brother, you should observe the prayer at its prescribed fixed time and not be preoccupied by the matters of this world because the prayer gives comfort to the believers as mentioned in sound Hadith.
The Prophet said: “The delight of my eye lies in performing the prayer”. [Ahmad and An-Nasaa’i]
Another narration reads: “Comfort us (with the prayer) o Billal! (i.e. by calling to the prayer”. [Abu Dawood].
As regards the oath that you made, if your intention was to perform the prayer in congregation and you did not, then you are obliged to expiate even though you were ignorant or forgetful. But, if your intention was to perform the prayer at its prescribed fixed time, then nothing would be imposed upon you.
Anyway, you can expiate for your oath by: (a) Feeding ten needy people, or (b) clothing them, or (c) Freeing a slave. However, if you are unable to do any of the above, you are allowed to fast for three days as an atonement.
Allah knows best.