Allah says;
إِنَّا سَخَّرْنَا الْجِبَالَ مَعَهُ يُسَبِّحْنَ بِالْعَشِيِّ وَالاِْشْرَاقِ
Verily, We made the mountains to glorify Our praises with him in the `Ashi and Ishraq.
means, Allah caused the mountains to glorify His praises with him at sunrise and at the end of the day.
This is like the Ayah;
يَجِبَالُ أَوِّبِى مَعَهُ وَالطَّيْر
O you mountains. Glorify (Allah) with him! And you birds (also)! (34;10)
The birds also used to glorify Allah's praises with him. If a bird flew by him and heard him chanting the Zabur, it would not go away; instead it would stay hovering in the air, glorifying Allah along with him. And the lofty mountains would respond to him and echo his glorification of Allah.
Ibn Jarir recorded from Abdullah bin Al-Harith bin Nawfal that,
Ibn Abbas, may Allah be pleased with him, did not pray Ad-Duha. (Abdullah said;) "So I took him to Umm Hani, may Allah be pleased with her, and said to her, `Tell him what you told me.'
She said, `The Messenger of Allah entered my house on the day of the conquest of Makkah. He called for water to be poured into a large bowl, then he called for a garment which he used as a screen between me and him, and he washed himself. Then he sprinkled water around the house and prayed eight Rakahs. This was Ad-Duha, and its standing, bowing, prostration and sitting were all equal in brevity.'
Ibn Abbas, may Allah be pleased with him, left, saying,
`I have read the Qur'an from cover to cover, and I never knew about Salat Ad-Duha until now!'
Then he recited;
يُسَبِّحْنَ بِالْعَشِيِّ وَالاِْشْرَاقِ
(glorify Our praises with him in the `Ashi and Ishraq).
I used to say, "What is Salat Al-Ishraq, but now I know what it is.