980/1 - Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah’s peace and blessings be upon him) said: “Three supplications are undoubtedly answered: the supplication of the oppressed, the supplication by a traveler, and the supplication of a parent against his child.”
[Narrated by Abu Dāwūd and Al-Tirmidhi, who classified it as Hasan (sound)]. The version by Abu Dāwūd does not contain: “against his child”.
1) The supplication of an oppressed person is readily answered, if he supplicates against his oppressor to suffer something similar to or less than the harm he inflicted upon him. If he supplicates beyond that, he has thus transgressed. Allah Almighty answers the supplication of an oppressed person, even if he is a disbeliever, not out of love for him, but out of love for justice.
2) We are urged to seize the opportunity for supplication during travel. This is because a traveler is in temporary need, and when a person in need supplicates his Lord, He responds to him.
3) The supplication of a parent, whether it is the father or mother, for or against his child is readily answered. As for his supplication for his child, it is answered because he makes it out of mercy and compassion towards him. His supplication against him is answered because the parent would not supplicate against his child except if the child deserves it.