Sahih al-Bukhari 818, 819

Narrated Abu Qilaba:Once Malik bin Huwairith said to his friends, "Shall I show you how Allah's Messenger (ﷺ) used to offer his prayers?" And it was not the time for any of the compulsory congregational prayers. So he stood up (for the prayer) bowed and said the Takbir, then he raised his head and remained standing for a while and then prostrated and raised his head for a while (sat up for a while). He prayed like our Sheikh `Amr Ibn Salama. (Aiyub said, "The latter used to do a thing which I did not see the people doing i.e. he used to sit between the third and the fourth rak`a). Malik bin Huwairith said, "We came to the Prophet (after embracing Islam) and stayed with him. He said to us, 'When you go back to your families, pray such and such a prayer at such and such a time, pray such and such a prayer at such and such a time, and when there is the time for the prayer then only of you should pronounce the Adhan for the prayer and the oldest of you should lead the prayer."