How did earlier prophets before Muhammed (PBUH) worship Allah ? Was there Salah during the period of Adam(PBUH), was it mandatory to offer Prayers for them ?
Of course it was, see the Qura'n:
Our Lord, I have settled some of my descendants in an uncultivated valley near Your sacred House, our Lord, that they may establish prayer. So make hearts among the people incline toward them and provide for them from the fruits that they might be grateful.14:37
My Lord, make me an establisher of prayer, and [many] from my descendants. Our Lord, and accept my supplication. [14:40]
And He has made me blessed wherever I am and has enjoined upon me prayer and zakah as long as I remain alive [19:31]
So the angels called him while he was standing in prayer in the chamber, "Indeed, Allah gives you good tidings of John, confirming a word from Allah and [who will be] honorable, abstaining [from women], and a prophet from among the righteous." 3:39
and many more.
In addition, the prayer did look like ours:
And [mention] when We made the House a place of return for the people and [a place of] security. And take, [O believers], from the standing place of Abraham a place of prayer. And We charged Abraham and Ishmael, [saying], "Purify My House for those who perform Tawaf and those who are staying [there] for worship and those who bow and prostrate [in prayer]." 2:125
O Mary, be devoutly obedient to your Lord and prostrate and bow with those who bow [in prayer]."3:43
From these verses we know that the prayers did contain bowing and prostrating. But we don't know exactly how it was.
yes all the prophets before muhammad s.a.w. off course PRAYED to god. but the method and techniques were not thought to us how did they exactly pray. but ancient sources said that prophets before muhammad s.a.w. like jesus as., moses as., noah as., adam as., abraham as., etc "PROSTRATED" to god in a way to pray/worship god. it proves that the movement to bow and prostrate like how we do now in salah has ancient roots that god appointed every prophet to prostrate to him. and the main purpose of the worship/ibadah which u can say "salat" is exactly to show servitude to allah swt which was done by all the prophets.
there is no specific method for worshipping... all sources ancient or not is tampered with. it cannot be trusted. men use to worship men bowing and prostrating to them...others kneeled... others went flat on their stomachs... the Quran states.... you can WORSHIP ME in ANY FORM. Go do some homework. after all millions of MUSLIMS have never ever read the Quran... his own book from start to finish to try to comprehend what is says or has to offer... including "PRACTISING MUSLIMS".