I'd like to know how pray for forgiveness from Allaah for the mistakes done your life? How to behave when you sometime have companions who always talk about other people.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Asking forgiveness from Allaah has some etiquettes and certain expressions which one should be heedful of. From among the expressions of forgiveness one should ask his Lord by are: "Allaahumma Ghfirly" (O Allaah! Forgive me), "Allaahumma Tub 'Alayya" (O Allaah! Accept my repentance), and similar Du'aa' for forgiveness.

The best expression for asking forgiveness is what is reported in the book of Imaam Al-Bukhari from Shaddaad Ibn Aws, that the Prophet said: "The most superior way of asking for forgiveness from Allaah is: 'Allaahumma anta Rabbi laa ilaaha illa anta, Khalaqtani wa ana 'abduka, wa ana 'ala 'ahdika wa wa'dika mastata'tu, A'uthu bika min Sharri ma sana'tu, aboo'o Laka bini'matika 'alayya, wa Aboo'o bithanbi faghfirli innahu laa yaghfiru ath-thu noobu illa anta.' (O Allaah! You are my Lord, none has the right to be worshipped except You, You created me and I am Your servant, and I abide to Your covenant and promise as best I can, I take refuge in You from the evil of which I have committed. I acknowledge your favor upon me and I acknowledge my sin, so forgive me, for verily none can forgive sin except you). The Prophet added. "If somebody recites it during the day with firm faith in it, and dies on the same day before the evening, he will be from the people of Paradise; and if somebody recites it at night with firm faith in it, and dies before the morning, he will be from the people of Paradise." [Al-Bukhari]

Another plea of forgiveness is reported by Abu Daawood and others from Ibn 'Umar who said: "We counted that the Apostle of Allaah () would say a hundred times during a meeting: "My Lord, forgive me and pardon me; You are the Pardoning and Forgiving One."

It is also recommended to make ablution before asking forgiveness and raise both hands at the time of seeking forgiveness. The evidence is in the story of the companion Abu 'Aamir ('Ubayd the uncle of Abu Moosa al-Ash'ari ['Abdullaah ibn Qays]), may Allaah be pleased with both of them, during the battle of Awtaas that the Prophet called for the water, made ablution, raised his hands and said, "O Allaah! Forgive 'Ubayd, Abu Aamir." He also said once, "O Allaah! Forgive the sin of 'Abdullaah bin Qays." [Al-Hadeeth]  As for what is narrated from Ibn 'Abbaas "hands should be raised up during supplication, and pointing with the pointer finger is done when asking for forgiveness" is merely his saying which is not reported from the Prophet .  On the other hand, the narration of the Prophet clearly proves that one should raise his hands when asking forgiveness.

Whenever one seeks forgiveness he should do it attentively and with purpose. The Prophet said: "Allaah does not respond to the supplications made by an inattentive and careless heart." This is a good narration reported by At-Tirmithi.

As for the prayer of repentance read our Fatwa: 84513.

When dealing with those who talk about others in their absence, remember that backbiting is one of the grave sins. Allaah says (which means): {And do not spy or backbite each other. Would one of you like to eat the flesh of his brother when dead? You would detest it. And fear Allaah; indeed, Allaah is accepting of repentance and Merciful.}[Quran 49:12].

Therefore, whoever committed that sin should make sincere and immediate repentance before it is too late. It is mandatory on the one who hears backbiting should try to prevent the person from that sin as Allaah commands us in the Quran: {enjoin what is right, forbid what is wrong.}[Quran 31:17].

The Prophet said: "He who sees something abominable should change it with his hand (physically); and if he is unable to do so, then with his tongue (verbally), and if he is unable to do so, then he should (abhor it) from his heart, and this is the weakest level of faith." [Muslim]

Whenever, you hear someone backbiting, you should try to stop him/her from that act. If he listens to you, then all perfect praise to Allaah, otherwise you have to leave the place since leaving the place of evil is better than hearing backbiting. Allaah says (which means): {And when you see those who engage in [offensive] discourse concerning Our verses, then turn away from them until they enter into another conversation. And if Satan should cause you to forget, then do not remain after the reminder with the wrongdoing people.}[Quran 6:68]. Allaah also says (which means): {And when they hear ill speech, they turn away from it.}[Quran 28:55].

Imaam Ibn Al-'Arabi Al Maaliki said: "association with those who are involved in major sins is not allowed."

Backbiting is one of the major sins, so the one who hears it should silence the backbiter or leave the place.

Allaah knows best.