The command to show leniency

a) Make things easy for the people and do not make things difficult for them.

It has been narrated by Sa’d b. Abu Burda through his father through his grandfather that the Prophet of Allah (ﷺ) sent him and Mu’adh (on a mission) to the Yemen, and said (by way of advising them):
Show leniency (to the people) ; don’t be hard upon them; give them glad tidings (of Divine favours in this world and the Hereafter) ; and do not create aversion. Work in collaboration and don’t be divided.
Reference : Sahih Muslim 1733

an-Nawawi commented
وفي هذا الحديث : الأمر بالتبشير بفضل الله وعظيم ثوابه وجزيل عطائه وسعة رحمته ، والنهي عن التنفير بذكر التخويف وأنواع الوعيد محضة من غير ضمها إلى التبشير .
وفيه تأليف من قرب إسلامه وترك التشديد عليهم ، وكذلك من قارب البلوغ من الصبيان ، ومن بلغ ومن تاب من المعاصي كلهم يتلطف بهم ويدرجون في أنواع الطاعة قليلا قليلا ، وقد كانت أمور الإسلام في التكليف على التدريج فمتى يسر على الداخل في الطاعة أو المريد للدخول فيها سهلت عليه ، وكانت عاقبته غالبا التزايد منها ، ومتى عسرت عليه أوشك أن لا يدخل فيها ، وإن دخل أوشك أن لا يدوم أو لا يستحليها .
In short he says In this hadith there is an order of telling the fadhl of Allah, HIS great reward and Mercy, and prohibition of telling ONLY regarding fear, the punishment.
Same way leniency should be shown to youngsters and it should be mentioned tawbah clears all the sins [Sharah Sahih Muslim an-Nawawi, Kitab al Jihad under the chapter The command to show leniency and avoid causing aversion]

b) How bad and harsh were the opinions of khawarij.

Narrated Al-Azraq bin Qais:
We were in the city of Al-Ahwaz on the bank of a river which had dried up. Then Abu Barza Al- Aslami came riding a horse and he started praying and let his horse loose. The horse ran away, so Abu Barza interrupted his prayer and went after the horse till he caught it and brought it, and then he offered his prayer. There was a man amongst us who was (from the Khawari) having a different opinion. He came saying. “Look at this old man! He left his prayer because of a horse.” On that Abu Barza came to us and said, “Since the time I left Allah’s Messenger (ﷺ), nobody has admonished me; My house is very far from this place, and if I had carried on praying and left my horse, I could not have reached my house till night.” Then Abu Barza mentioned that he had been in the company of the Prophet, and that he had seen his leniency.
Reference : Sahih al-Bukhari 6127

Ibn Hajr commented:
وحكى ابن التين عن الداودي أن معنى قوله : ” له رأي ” يظن أنه محسن وليس كذلك . وقوله ” نضب عنه بالماء ” بنون وضاد معجمة ثم موحدة أي زال ، وقد تقدم في أواخر الصلاة بلفظ ” فجعل رجل من الخوارج يقول ” فهذا هو المعتمد ، وأن المراد بالرأي رأي الخوارج ، والتنوين فيه للتحقير ، أي رأي فاسد وقد تقدم شرح الحديث هناك .
Ibn at-Teen quoted from ad-Dawoodi that the meaning of “He had opinion” is He thought he is Mohsin (pious or Saaib al Raai) but actually he was not… it has already been mentioned previously in the narration of awakhir as-Slaat with the words: “A man from the Khawarij said”.. The meaning of “opinion: is the opinion of khawarij. This tanween is for tahqeer (i.e. denouncing) meaning (he had) a faasid opinion.. [Fath al Bari]

Imam al Bukhari mentioned this chapter under Book of Good Manners and Form (Al-Adab) Chapter: “Make things easy for the people and do not make things difficult for them.”

c) The Prophet’s (peace be upon him) advice to Aisha (The monther of believers)

Prophet peace be upon him said:
“A’ishah be lenient, for leniency makes a thing decorated and when it is removed from a thing it makes it defective.
Reference : Sunan Abi Dawud 2478

d) It is recommended to waive debts

A’isha (Allah be pleased with her) reported:
Allah’s Messenger (ﷺ) heard the voices of altercation of two disputants at the door; both the voices were quite loud. The one demanded some remission and desired that the other one should show leniency to him, whereupon the (other one) was saying: By Allah will not do that. Then there came Allah’s Messenger (ﷺ) to them and said: Where is he who swears by Allah that he would not do good? He said: Massenger of Allah, it is I. He may do as he desires.
Reference : Sahih Muslim 1557

e) The virute of giving more time to one who is suffering difficulty, and letting those go who are suffering difficulty and those who are well off

Abu Mas’ud (Allah be pleased with him) reported Allah’s Messenger (ﷺ) as saying:
A person from people who lived before you was called to account (by Allah at the Day of Judgment) and no good was found in his account except this that lie being a rich man had (financial) dealings with people and had commanded his servants to show leniency to the straitened ones. Upon this Allah, the Exalted and Majestic, said: We have more right to this, so overlook (his faults).
Reference : Sahih Muslim 1561