The Meaning of Good-heartedness
Salamah linguistically: the root sin, lam, and mim revolves around wellness and good health. Salamah is wellbeing, and that man is free from disability and harm.  Maqayis al-Lughah, Ibn Faris (3/90), Lisan al-`Arab, Ibn Manzur (12/289).
Sadr linguistically: is the forefront of all things. All that confronts one is sadr. The sadr of a channel is its highest point, and the sadr of a matter is its beginning.  al-`Ayn, al-Khalil (7/94); al-Muhkam, Ibn Sidah (8/282); al-Mu`jam al-Wasit, the Academy of the Arabic Language (1/509).
Salamat al-Sadr technically: is being secure from malice, rancour, and hate, and from all other illnesses of the heart and its ailments. It is being safe from everything that takes away from Allah, exalted.  Fi al-Suluk al-Islami al-Qawim, Ibn al-Shawkani (p. 121). The Difference between Good-heartedness and Vacancy (Balah) and Gullibility (Taghafful)
Good-heartedness is not wanting evil for others after recognising it as such. The heart is saved from wanting evil to befall others, but not from knowing it. This is the difference between it and vacancy and gullibility. The latter are a form of ignorance and lack of awareness. They are blameworthy since they indicate shortcoming. A person is praised for recognising evil and its harm, then based on that not intending it or inflicting it upon others. `Umar ibn al-Khattab, Allah be pleased with him, said: “I am neither sly nor can the sly trick me.”  al-Ruh, Ibn al-Qayyim (p. 243-244). Commandments of Good-heartedness and Encouragement towards it in the Qur’an and Sunnah
❖ Allah, exalted, says: “Those who came after them say, ‘Lord, forgive us our sins and the sins of our brothers who believed before us, and leave no rancour in our hearts towards those who believe. Lord, You are truly compassionate and merciful.’” al-Hashr: 10
❖ Allah, exalted, says: “We shall have removed all rancour from their hearts; streams will flow at their feet. They will say, ‘Praise be to Allah, who guided us to this: had Allah not guided us, We would never have found the way. The messengers of our Lord brought the Truth.’ A voice will call out to them, ‘This is the Garden you have been given as your own on account of your deeds.’” al-A`raf: 43
❖ `Abdullah ibn Mas`ud, Allah be pleased with him, said: “The Messenger of Allah ﷺ said: ‘Let none of my companions tell me something about someone. I like that I come out to you with a sound conscience.’”  Reported by Abu Dawud (4860) and this is his wording, as well as al-Tirmidhi (3896) and Ahmad (3759). al-Tirmidhi said: “It is strange from this transmittance.” Ahmad Shakir said in his analysis of Musnad Ahmad (5/286): “Its chain is at least sound.” al-Albani weakened it in Da`if Sunan Abi Dawud (4860).
❖ `Abdullah ibn `Amr, Allah be pleased with them both, said: “It was said to Allah’s Messenger ﷺ: ‘Who is best among people?’ He replied: ‘One with a clean heart and a truthful tongue.’ They said: ‘We know what it means to be truthful; what type of person is he of a clean heart?’ He replied: ‘It is the pious, pure one. He has no sin against him nor transgression, and he holds no rancour nor envy.’”  Reported by Ibn Majah (4216) and this is his wording, as well as al-Bayhaqi in Shu`ab al-Iman (6604). al-Mundhari authenticated its chain in al-Targhib wa al-Tarhib (4/33), and likewise al-Busiri in Zawa’id Ibn Majah (2/325), al-`Iraqi in Takhrij al-Ihya’ (3/18), and al-Albani in Sahih Sunan Ibn Majah (4216). Quotes of the Predecessors and Scholars on Good-heartedness
❖ Ibn al-`Arabi said: “The heart is not sound if it is hateful, envious, self-amazed, and arrogant. The Prophet ﷺ made it a condition for faith that one loves for his brother what he loves for himself.”  Ahkam al-Qur’an, Ibn al-`Arabi (3/459).
❖ Shaykh al-Islam said: “The sound, praiseworthy heart is the one that wants good, not evil. As for the one that does not know evil then this is a flaw that is blameworthy.”  al-Fatawa al-Kubra, Ibn Taymiyyah (5/264). Benefits of Good-heartedness
It is a means for entering the Garden. Allah, exalted, says: “the Day when neither wealth nor children will be of any benefit. Only those who come before Allah with a pure heart will be saved.” al-Shu`ara’: 88 - 89. It makes its possessor the best of people. It leads the heart to goodness, righteousness, obedience, and rectification, to a degree where it finds no rest but in these things, nor delight except in engaging them. It removes faults and severs the means to sin. Whoever’s heart is sound and pure from corrupt desires and doubtful uncertainty, his tongue and limbs will cease from all ugly deeds. Forms of Good-heartedness
Having good-heartedness with the masses. He holds no rancour nor envy in his heart for them, nor any other of the heart’s ailments that destroy love and care for others. Having good-heartedness with those close to him. Having good-heartedness with rulers. He has no ill feelings towards them, does not incite the masses against them, and does not mention their slip-ups in front of them. Rather he advises them, has sympathy for them in their position, overlooking their mistakes which may be overlooked, spreads good things about them, and mentions them in good standing. Rulers having sound hearts with those whom they rule. They are not suspicious of them, nor wait for them to slip up nor spy on them, and they do not harm them in their wealth and property. Instead, they have pity for them and seek out the means to their comfort. Teachers and students having sound hearts with each other.  Ma`alim Tarbawiyya li-Talibi Asna al-Wilayat al-Shar`iyyah, Muhamad Mukhtar al-Shinqiti (p. 64). Barriers to Acquiring Good-heartedness
The whispers of Satan and his enticements. The devil is keen to cause ill feelings between brothers and corrupt hearts. The heart being afflicted by some deadly spiritual ailment, corrupting it, like envy, rancour, and malice. Competition for the worldly life. Love of fame and power. It is an overpowering, dangerous, and potentially terminal spiritual sickness. Being characterised by some qualities that cloud the chests of men and compromise their soundness, like excessive joking, abundant argumentation, self-amazement, and others. Means to Acquiring Good-heartedness
Sincerity with Allah. Keenness with the Book of Allah - reciting, learning about, and teaching it. It is a cure for what is in the hearts. Supplication. It is the sure cure and the definite treatment. The slave pleads his Lord to give him soundness of heart. Having mannerisms and holding morals that increase amiability and love among the believers. Like being cheerful, smiling, spreading greetings, giving each other gifts, and others. These mannerisms suffice as a cause to remove bitterness and ill feelings within one’s heart, and for it to become clean and pure. Contentment with what Allah has decreed.  Madarij al-Salikin, Ibn al-Qayyim (2/201) Examples of Good-heartedness from the Life of the Companions and Predecessors
❖ Zayd ibn Aslam narrates that “he entered upon Abu Dujanah while he was ill, yet his face was glowing with happiness. He asked him: ‘How come your face is happy?’ He replied: ‘I have no greater trust than in two deeds of mine: I never spoke about what did not concern me, and my heart was always sound towards the Muslims.’”  Reported by Ibn Sa`d in al-Tabaqat al-Kubra (4577) and Ibn Abi al-Dunya in al-Samt (113).
❖ It is narrated from Abu al-Darda’ that he used to supplicate for seventy of his companions, naming them by name. This is a sign of a sound heart.  Ibn Battal mentioned it in Sharh Sahih al-Bukhari (2/450).
❖ al-Fadl ibn Abi `Ayyash said: “I was sitting with Wahb ibn Munabbih, then a man came to him and said: ‘I passed by so-and-so and he was cursing you.’ He was angered by this and said: ‘Did the devil find no messenger other than you?’ I had only left Wahb briefly, then that man who had cursed him came to him and greeted Wahb, to which Wahb replied, extended his hand, shook it, and sat him next to him.”  Safwat al-Safwah, Ibn al-Jawzi (1/457). Good-heartedness in Poetry
“He does not carry malice, one who is lofty
Nor does he reach high stations, the oft-angry.”  Majani al-Adab fi Hada’iq al-`Arab, Rizqullah Shaykhu (5/251).