I made a vow that once I get a job that pleases my family, I will give 20 dinars of my salary per month in charity to the needy. Having got the job, can I consider my act of giving the sum per month a continuous charity or it is just a fulfillment of a vow and thus I will only receive its reward?

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, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

In the Quran, Allaah Almighty praised those who fulfill their vows, saying (what means): {They [are those who] fulfill [their] vows and fear a Day whose evil will be widespread.} [Quran 76: 7]

In a Hadeeth, the Prophet, sallallaahu ‘alayhi wa sallam, dispraised those who do not fulfill their vows, saying: "The best of you are my generation, then those who follow them, then those who will come after them. Then they will be followed by those who will make vows but will not fulfill them." [Al-Bukhari]

Since fulfillment of vows is an asserted obligation, it is illogical that charity, which is a voluntary act of worship, would be greater than it in terms of reward or earning the love of Allaah and His satisfaction.  The Prophet, sallallaahu ‘alayhi wa sallam, related in a Hadeeth Qudsi that Allaah Almighty said:

"My servant draws not near to Me with anything more loved to Me than (by fulfilling) the religious duties I have enjoined upon him, and My servant continues to draw near to Me by doing voluntary acts of worship until I love him. When I love him, I will be his hearing with which he hears, his sight with which he sees, his hand with which he strikes, and his foot with which he walks. Were he to ask [something] of Me, I would surely give it to him, and were he to ask Me for refuge, I would surely grant him it." [Al-Bukhari]

Allaah Knows best.