Repeating the du’a three times is a recommended action because it shows a sense of urgency in obtaining what you are asking for. We see this in the example of our beloved Prophet Muhammad, peace and blessings of Allah be upon him. Ibn Mas’ud, may Allah be pleased with him, reported: “When the Prophet, peace be upon him, finished his prayer, he raised his voice, and prayed against them (the leaders of the Quraysh who had persecuted him). And whenever he made du’a, he would repeat it thrice, and whenever he asked (from Allah), he would do so thrice. So he, peace be upon him, then said:
“O Allah! Upon you is (the retaliation) of the Quraysh!
O Allah! Upon you is (the retaliation) of the Quraysh!
O Allah! Upon you is (the retaliation) of the Quraysh!”
(Recorded in al-Bukhari)
Anas ibn Malik also reported that the Prophet, peace be upon him, said:
“Whoever asks for Paradise three times, Paradise says: ‘O Allah! Enter him into Paradise!’ And whoever seeks refuge from the Hellfire three times, the Hellfire says: ‘O Allah! Save him from the Hellfire!” (Recorded in al-Tirmidhi)