Sahih Muslim
The Book Pertaining to Repentance and Exhortation to Repentance (Kitab Al-Tauba)
Book Number: 037 / Hadith Number: 6634
Salman reported that Allah's Messenger (may peace be upon him) said: Verily, Allah created, on the same very day when He created the heavens and the earth, one hundred parts of mercy. Every part of mercy is coextensive with the space between the heavens. and the earth and He out of this mercy endowed one part to the earth and it is because of this that the mother shows affection to her child and even the beasts and birds show kindness to one another and when there would be the Day of Resurrection, Allah would make full (use of Mercy).