Hadith: No Muslim on earth supplicates Allah, the Almighty, except that Allah answers his supplication or averts from him harm equivalent to it, unless he supplicates for something sinful or for the severing of the ties of kinship
عن عبادة بن الصامت رضي الله عنه و أبي سعيد الخدري رضي الله عنه مرفوعاً: «ما على الأرض مسلم يدعو الله تعالى بدعوة إلا آتاه الله إياها، أو صرف عنه من السوء مثلها، ما لم يَدْعُ بإثم، أو قطيعة رحم»، فقال رجل من القوم: إذا نُكثِر قال: «اللهُ أكثر». وفي رواية أبي سعيد زيادة:«أو يَدَّخر له من الأجر مثلها». [صحيح] - [رواه الترمذي، وبالزيادة رواه أحمد] المزيــد ...
‘Ubādah ibn As-Sāmit and Abu Sa‘īd al-Khudri (may Allah be pleased with both of them) reported that the Prophet (may Allah's peace and blessings be upon him) said: "No Muslim on earth supplicates Allah, the Almighty, except that Allah answers his supplication or averts from him harm equivalent to it, unless he supplicates for something sinful or for the severing of the ties of kinship." Upon this one of the Companions said: "Then we shall supplicate plenty." He said: "Allah is more plentiful (in responding)."
The report of Abu Sa‘īd al-Khudri had the following addition:"Or Allah will save an equivalent reward for him." Sahih/Authentic. - [At-Tirmidhi]
This Hadīth encourages every Muslim to have a connection with Allah, Exalted and Glorified, in words and deeds. The supplication that comes out of a sincere heart that is filled with love for Allah will find the gates of heaven open before it. It will be answered by Allah Who answers the one in distress when he calls upon Him and removes hardship. Supplication is never wasted; it will either be answered, or Allah will prevent harm from befalling the person in proportion to the supplication, or He will save reward for him in the Hereafter equivalent to the supplication. Verily, what Allah has of goodness is way more than what people could ever ask for.