Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: When the day had advanced, the Messenger of Allah (peace and blessings be upon him) would go out to one of the gardens of Madinah, where water for ablution would be made ready for him (peace and blessings be upon him). If he (peace and blessings be upon him) had a need, he would relieve it; otherwise he would perform ablution. Then, when the sun had declined from the zenith of the sky by the length of a sandal strap, he (peace and blessings be upon him) would stand and pray four rak'ahs, not sitting for the tashahhud between them and giving the salam at the end of the four; then he would go to the mosque. Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: I said: "O Messenger of Allah, what is this prayer that you pray and we do not pray?" He (peace and blessings be upon him) said: "Whoever of my Ummah prays these four rak'ahs has brought to life an hour of his night, in which the gates of heaven are opened and supplication is answered."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11316