Why do people pray to Buddhas? Why do Buddhists pray to Buddhas in temples? I heard that Sakyamuni didn't approve of that and even criticized Bodhisattva for telling other people that he can help them with things that only God can help with. Sakyamuni considered himself and Bodhisattva as ordinary human beings without any divine abilities. Is that true? Is there any reference or source which confirms this?
Buddhists don't praying Buddha. Not reciting chants as devotee does for other gods. 
We just ignite candle which is symbol of enlightenment and we just pay homage to Buddha, Dhamma and Sangha those are Three Jewels.
Faith in Buddhism centres on belief in the Three Jewels.


  Buddhaṃ saraṇaṃ gacchāmi.
      Dhammaṃ saraṇaṃ gacchāmi.
      Saṅghaṃ saraṇaṃ gacchāmi.  
  
  I take refuge in the Buddha.
      I take refuge in the Dharma.
      I take refuge in the Sangha.


Buddhist don't believe in god and Buddha never said anything about god.
So he criticized because of distracting people which Buddha never mentioned this in his techniques or what people supposed him as (that god is exist and can help someone with something) so he wasn't god just ordinary human being like us.
But he enlightened one and became Buddha.

There's Buddha delivered discourse Jewels  in Ratana Sutta  

Ratana Sutta  

*RATANA SUTTA
The Buddha’s Discourse on
The Three Superb Jewels
And Their Intrinsic Power   

With an Introduction, Translation,  and
 Explanations Based on Pali Sources by
Bhikkhu Nanadassana

1.Yànãdha bhåtàni samàgatàni,
Bhummàni và yàni va antalikkhe,
Sabbe'va bhåtà sumanà bhavantu,
Atho' pi sakkacca suõantu bhàsitaŋ.  


  1.Whatever beings are here assembled,
  Whether terrestrial or celestial,
  May all beings be glad.
  Moreover,may they attentively
  Listen to what is said:  


2.Tasmà hi bhåtà nisàmetha sabbe,
Metta ŋkarotha mànusiyà pajàya,
Divà ca ratto ca haranti ye baliŋ,
Tasmà hi ne rakkhatha appamattà.  


  2.Therefore, pay heed all you beings,
  Show your friendliness to humankind,
  Who day and night bring you offerings.
  Hence, protect them diligently.  


3.Yaŋ ki¤ci vittaŋ idha và huraŋ và
Saggesu và yaŋ ratanaŋ paõãtaŋ
Na no samaŋ atthi Tathàgatena.
Idam'pi Buddhe ratanaŋ paõãtaŋ.
Etena saccena suvatthi hotu!  

Suvatthi(su-"good, well"+atthi"to be, being") = well-being
:good  health  or  fortune.
Or  as  the  Commentary  ex-plains: arogatā (healthiness), 
nirupaddavatā (no  danger, safety).  


  3.Whatever treasure there is here or beyond,
  Or whatever superb jewel is in the heavens,
  None is equal to the Tathàgata (the Buddha).
  Verily, in the Buddha is this superb jewel.
  By virtue of this truth may there be well-being!  


4.Khayaŋ viràgaŋ amataŋ paõãtaŋ
Yadajjhagà Sakyamunã samàhito
Na tena Dhammena samatthi ki¤ci.
Idam'pi Dhamme ratanaŋ paõãtaŋ.
Etena saccena suvatthi hotu!  


  4.There is nothing equal to that Dhamma
  Of the superb Extinction (of defilements),
  Dispassion, and Deathlessness (Nibbàna),
  Which the concentrated Sakyan Sage (the Buddha) has realized.
  Verily, in the Dhamma is this superb jewel.
  By virtue of this truth may there be well-being!  


5.Yaŋ Buddhaseññho parivaõõayã suciŋ
Samàdhim'ànantarika¤'¤am'àhu.
Samàdhinà tena samo na vijjati.
Idam'pi Dhamme ratanaŋ paõãtaŋ.
Etena saccena suvatthi hotu!  


  5.That Purity which the Supreme Buddha extolled
  Is called "concentration with immediate effect".
  Nothing equal to that concentration is found.
  Verily, in the Dhamma is this superb jewel.
  By virtue of this truth may there be well-being!  


6.Ye puggalà aññha sataŋ pasatthà
Cattàri etàni yugàni honti.
Te dakkhiõeyyà Sugatassa sàvakà,
Etesu dinnàni mahapphalàni
Idam'pi Saïghe ratanaŋ paõãtaŋ.
Etena saccena suvatthi hotu!


  6.Those eight individuals
  That are praised by the Virtuous Ones
  Constitute the four pairs (of persons).
  They, the worthy of offerings, 
  Are the disciples of the Well-farer (the Buddha),
  And gifts given to them yield abundant fruit.
  Verily, in the Saïgha is this superb jewel.
  By virtue of this truth may there be well-being!  


7.Ye suppayuttà manasà daëhena,
Nikkàmino Gotamasàsanamhi,
Te pattipattà amataŋ vigayha,
Laddhà mudhà nibbutiŋ bhu¤jamànà.
Idam'pi Saïghe ratanaŋ paõãtaŋ.
Etena saccena suvatthi hotu!  


  7.Those who with a steadfast mind,
  Apply themselves well
  In the Buddha Gotama's Teaching,
  Being desireless, attain the highest gain.
  They plunge into the Deathlessness (Nibbàna)
  And enjoy the peace of emancipation,
  Obtained for free.
  Verily, in the Saïgha is this superb jewel.
  By virtue of this truth may there be well-being!  


8.Yathindakhãlo pañhaviŋ sito siyà
Catubbhi vàtehi asampakampiyo,
Tathåpamaŋ sappurisaŋ vadàmi,
Yo ariyasaccàni avecca passati.
Idam'pi Saïghe ratanaŋ paõãtaŋ.
Etena saccena suvatthi hotu!  


  8.Just as a city-post fixed firmly in the ground
  Is unshake able by the four winds,
  So too, I declare, is the virtuous person
  Who sees the Noble Truths unwaveringly.
  Verily, in the Saïgha is this superb jewel.
  By virtue of this truth may there be well-being!  


9.Ye Ariyasaccàni vibhàvayanti,
Gambhãrapa¤¤ena sudesitàni,
Ki¤càpi te honti bhusappamattà
Na te bhavaŋ aññhamaŋ àdiyanti.
Idam'pi Saïghe ratanaŋ paõãtaŋ.  


  9.Those who clearly comprehend the Noble
  Truths, Well taught by him of profound wisdom
  Even if they are very negligent,
  They do not take up an eighth rebirth.
  Verily, in the Saïgha is this superb jewel.
  By virtue of this truth may there be well-being!  


10.Sahàvassa dassanasampadàya
Tayassu dhammà jahità bhavanti:
Sakkàyadiññhi, vicikicchita¤ca
Sãlabbataŋ và'pi yadatthi ki¤ci.
Catåhapàyehi ca vippamutto,
Cha càbhiñhànàni abhabbo kàtuŋ.
Idam'pi Saïghe ratanaŋ paõãtaŋ.
Etena saccena suvatthi hotu!  


  10.Just with his gaining of insight
  He abandons three states of mind:
  Self-identity view, sceptical doubt,
  And whatsoever [grasping to]
  Mere rules and observances.
  He is also fully freed from (rebirth in)
  The four woeful worlds (apàyas),
  And is incapable of committing
  The six major misdeeds.
  Verily, in the Saïgha is this superb jewel.
  By virtue of this truth may there be well-being!  


11.Ki¤càpi so kammaŋ karoti pàpakaŋ
Kàyena vàcà uda cetasà và,
Abhabbo so tassa pañicchàdàya,
Abhabbatà diññhapadassa vuttà.
Idam'pi Saïghe ratanaŋ paõãtaŋ.
Etena saccena suvatthi hotu!  


  11.Any evil action he may still commit
  By body, speech, or mind,
  He is incapable of concealing it;
  For it is said that such incapability
  Is of one who has seen the Path (of Nibbàna).
  Verily, in the Saïgha is this superb jewel.
  By virtue of this truth may there be well-being!  


12.Vanappagumbe yathà phussitagge
Gimhànamàse pañhamasmiŋ gimhe,
Tathåpamaŋ 
Dhammavaraŋ ade sayã,
Nibbànagàmiŋ paramaŋ hitàya.
Idam'pi Buddhe ratanaŋ paõãtaŋ.
Etena saccena suvatthi hotu!  


  12.As a woodland grove is crowned 
  With blossoming flowers
  During the heat of the first month of the summer,
  Even so (crowned) is the sublime Dhamma
  Leading to Nibbàna which
  He (the Buddha)
  Expounded for the highest good.
  Verily, in the Buddha is this superb jewel.
  By virtue of this truth may there be well-being!  


13.Varo, vara¤¤å, varado, varàha ro,
Anuttaro Dhammavaraŋ adesayã.
Idam'pi Buddhe ratanaŋ paõãtaŋ.
Etena saccena suvatthi hotu!  


  13.He, the Sublime one (the Buddha),
  The Knower of the Sublime (Nibbàna),
  The Giver of the Sublime (Dhamma),
  The Bringer of the Sublime (Noble Path),
  The Peerless one (the Buddha)
  Taught the Sublime Dhamma.
  Verily, in the Buddha is this 
  superb jewel.
  By virtue of this truth may there be well-being!  


14.Khãõaŋ puràõaŋ, navaŋ natthi sambhavaŋ
Virattacittà àyatike bhavasmiŋ,
Te khãõabãjà aviråëhicchandà,
Nibbanti dhãrà yathàyaŋ padãpo.
Idam'pi Saïghe ratanaŋ paõãtaŋ.
Etena saccena suvatthi hotu!  


  14.Their old (kamma) is destroyed,
  No new (kamma) is produced,
  And their mind is unattached to future rebirth.
  Those wise ones,with the seed (of rebirth-consciousness) destroyed,
  And with no more desire for further growth,
  Go out as the flame of a lamp.
  Verily, in the Saïgha is this superb jewel.
  By virtue of this truth may there be well-being!  


(Spoken by Sakka, Lord of the gods)

15.Yànãdha bhåtàni samàgatàni,
Bhummàni và yàni và antalikkhe,
Tathàgataŋ devamanussapåjitaŋ,
Buddhaŋ namassàma.
Suvatthi hotu!  


  15.Whatever beings are here assembled,
  Whether terrestrial or celestial,
  Let us revere the perfect Buddha
  Honoured by gods and men.
  May there be well-being!  


16.Yànãdha bhåtàni samàgatàni,
Bhummàni và yàni và antalikkhe,
Tathàgataŋ devamanussapåjitaŋ,
Dhammaŋ namassàma.
Suvatthi hotu!  


  16.Whatever beings are here assembled,
  Whether terrestrial or celestial,
  Let us revere the perfect Dhamma
  Honoured by gods and men.
  May there be well-being!  


17.Yànãdha bhåtàni samàgatàni,
Bhummàni và yàni và antalikkhe,
Tathàgataŋ devamanussapåjitaŋ,
Saïghaŋ namassàma. Suvatthi hotu!  


  17.Whatever beings are here assembled,
  Whether terrestrial or celestial,
  Let us revere the perfect Saïgha
  Honoured by gods and men.
  May there be well-being!